Thomas Aquinas and Romans 1: Natural Knowledge of God
Short answer: Thomas Aquinas (c. 1225-1274) read Romans 1:18-23 as a statement about what creation discloses and what sin suppresses. Paul says God's invisible attributes are perceived through the things that are made, so that those who reject him are without excuse, while the passage says the nations became futile in their reasoning and exchanged God's glory for images. Aquinas took that seriously in two directions: genuine knowledge of God is available to every human reason, and that knowledge is not saving. Grace and revelation remain necessary, because the same passage describes a mind darkened by unrighteousness. Aquinas never claimed philosophy could replace the gospel; he claimed creation leaves no one with a valid excuse. He did, however, build an entire theological method on the assumption that the same God speaks in nature and in Scripture.
The Context of Romans 1:18-23 in Paul's Argument
Paul has just announced that the gospel is God's power for salvation to everyone who believes, and that in it God's righteousness is revealed from faith to faith. Then he turns abruptly, in verse 18, to the opposite revelation: the wrath of God is revealed from heaven against ungodliness. The word revealed matters. Paul is not speculating about a hidden divine mood; he is describing something presently disclosed. The following verses explain the mechanism: what can be known about God is plain to the nations, because God made it plain, and the creation itself is the medium of that disclosure. Aquinas read this as the apostolic charter for natural theology, the disciplined study of what can be known of God from created things.
Notice, though, the surrounding argument. Paul is not writing a treatise on epistemology. He is building a case that all humanity, Jew and Greek alike, stands guilty before God and needs the righteousness that comes by faith. Romans 1:18-23 is the gentile half of that case; Romans 2 turns to the Jew. If the passage is read only as a proof text for the possibility of natural theology, its pastoral edge is lost. Paul's aim is to shut every mouth, not to congratulate philosophers. Aquinas knew this. His use of the passage serves his theology of grace, not a replacement for it.
The verbs Paul chooses are worth slowing down for. The nations knew God, he says, but they did not glorify him as God or give thanks; they became vain in their reasoning, and their senseless heart was darkened. This is not a story of honest ignorance. It is a story of knowledge held down, of truth suppressed in unrighteousness. Aquinas took the cognitive language seriously: the problem is not merely moral failure but a darkened mind. That is why he insisted that sin damages the very faculty by which God might be known, even as he insisted that the faculty and its object remain real.
Finally, the exchange language is central: they exchanged the glory of the incorruptible God for images resembling corruptible man, birds, animals, and creeping things. Idolatry is not primitive confusion in Paul's account; it is a trade, a deliberate swap of the Creator for created things. Aquinas lived in a world saturated with images, relics, and popular devotion, and he wrote against superstition as vigorously as against unbelief. The passage gave him language for both errors: the mind that denies God and the mind that worships something less than God are finally the same rebellion.
What Aquinas Meant by Natural Theology
When Aquinas speaks of natural theology, he means the knowledge of God that reason can reach from creatures, without the aid of special revelation. Romans 1 supplied him with the biblical warrant: the invisible things of God are understood through the things that are made. In the Summa Theologiae he argued that God's existence can be demonstrated from effects we observe, not because God is obvious, but because creatures depend on a cause that is not themselves. This is not a claim that everyone reasons it out consciously. It is a claim about what is genuinely available to a mind functioning as a mind.
He distinguished carefully between knowing that God is and knowing what God is. Reason, at its best, can establish that a first cause exists, that it is not composed of parts, that it is the source of all being, goodness, and order. It cannot tell us that God is triune, that he became flesh, or that he justifies the ungodly by faith. Those truths come by revelation and are received by faith. Aquinas was not blurring that line; he was protecting it. Romans 1 tells him the line exists, because the passage concerns what is perceived from creation, not the gospel hidden in God's counsel.
This distinction explains why Aquinas could write so confidently about pagan philosophers. He believed that truth is one, wherever it is found, because all truth has its source in God. If Aristotle correctly describes causation or virtue, then Aristotle has spoken truth, and truth belongs to the church even when the speaker does not. Romans 1 underwrote that confidence: whatever genuine knowledge of God exists among the nations exists because God made it plain. Aquinas did not treat pagan insight as neutral. He treated it as borrowed light, real but fragmentary.
Yet he never confused the borrowed light with the sun. The same theologian who wrote five ways to demonstrate God's existence wrote at length about the necessity of grace for the vision of God, about faith as a gift, and about the sacraments as means by which God works. If natural theology is read as Aquinas's whole theology, he is misrepresented. If it is read as one room in a larger house, the proportions come right: creation speaks, and Scripture speaks more clearly, and both speak of the same God.
Suppressing the Truth: Aquinas on Sin and the Mind
Romans 1:18 says men suppress the truth in unrighteousness. That word suppress is active. It describes resistance, not vacancy. Aquinas took this as a description of the fall's noetic effects: sin does not merely make us guilty, it damages our capacity to see what is there. The intellect is not destroyed, but it is disordered by disordered loves. We do not reason in a moral vacuum. When the will clings to what God forbids, the mind finds arguments to match. Aquinas called this a kind of blindness, and he saw it as both judgment and self-inflicted wound.
This is why his account of unbelief is not condescending. Paul says the nations are without excuse, and Aquinas agrees, but he also insists that the darkness is culpable precisely because it is chosen. The problem with the fool who says in his heart there is no God is not that he lacks data. It is that he does not want the God the data reveals. Aquinas understood that arguments alone rarely cure a heart that has already decided what it will not have. This is a pastoral insight as much as a philosophical one.
And it cuts both ways. If sin darkens the mind, then the believer's mind is not automatically clear either. Aquinas wrote as a theologian who expected to be corrected, who submitted his work to the church, and who reportedly called his own writings straw compared to what he had glimpsed. That posture flows from Romans 1: if unrighteousness suppresses truth, then humility before revelation is not weakness but honesty. The creature who reasons best still reasons as a creature, and the redeemed creature still reasons as a redeemed sinner.
So Aquinas would not let Romans 1 be used as a club against unbelievers without turning it on believers first. Every mind suppresses something. Every heart exchanges glory for lesser things. The passage's indictment is universal before it is particular, which is exactly why Paul moves from it to the universal remedy. Natural theology, in Aquinas's hands, ends in doxology and repentance, not in smugness about how much we have figured out.
Grace and Revelation Beyond What Reason Reaches
Aquinas is often accused of making theology a philosophical exercise, but his structure is the opposite. He begins the Summa not with proofs but with the claim that human salvation requires revelation, because the end we are made for exceeds what reason can discover. Romans 1 describes knowledge that leaves us without excuse; it does not describe knowledge that saves. The knowledge of God available in creation is enough to condemn, not enough to rescue. That gap is where grace operates, and Aquinas builds his entire account of faith, hope, and love on that gap.
He also distinguishes what reason can prepare from what grace must give. Reason can show that faith is not absurd, that the gospel's claims are not self-contradictory, and that the God who reveals himself is consistent with the God creation discloses. Reason cannot generate faith. Thomas says faith is a virtue infused by God, an assent moved by the will under the influence of grace. The person who reasons his way to a first cause has not thereby become a Christian. He has become a person who knows more than he can honor without grace.
This is where Romans 1 and 1 Corinthians 1 meet. Paul says the word of the cross is foolishness to those who are dying, but to those being saved it is the power of God. Aquinas quotes that theme often: what is wisdom to God looks like folly to the world, and what the world calls wisdom cannot grasp what God has prepared. Natural theology does not remove the scandal of the cross. It may even sharpen it, because the more clearly one sees the majesty of the Creator, the stranger it seems that he would save by a crucified Messiah.
None of this makes Aquinas anti-reason. It makes him a theologian of two lights. Creation gives real light, and Scripture gives real light, and where they seem to conflict, the conflict is in our reading, not in God. That confidence let him write on Aristotle and on the Trinity, on politics and on prayer, without fear that truth would contradict truth. Romans 1 was his anchor: the God who speaks in Scripture is the God whose handiwork the heavens declare.
One of the most common mistakes in reading Romans 1 is to apply it only to the obvious pagan. Paul's argument will not allow that. The indictment in verses 18-23 sweeps in every human being who has ever suppressed the truth, and the next chapter turns explicitly to those who judge others while doing the same things. Aquinas saw this and used the passage to describe the human condition, not a subclass of humans. The knowledge of God is universal; the suppression is universal; the guilt is universal. Only after that verdict does Paul announce the righteousness that comes by faith to all who believe.
This universal frame matters for how we use natural theology. Aquinas never imagined that the conclusions of reason could be set against the church's teaching as an independent authority. He imagined that the same God who made the mind also gave the revelation, so that whatever reason rightly concludes will be consistent with faith. Where it appears inconsistent, the fault lies in our reasoning or our reading. That is not a slogan for suppressing questions; it is a call to think harder and to submit more fully.
It also means the person who has never heard the gospel is not thereby innocent in Paul's account, and the person who has heard it is not thereby wise. Both need the same grace. Aquinas's theology of grace is often caricatured as a system of merit, but the whole point of his doctrine of grace is that merit itself is a gift, that God crowns his own gifts in us. Romans 1 provides the backdrop: if we are without excuse apart from grace, then everything we receive is mercy.
For readers today, this is practical. It means apologetics is not a matter of winning arguments but of addressing persons who suppress truth they already know at some level. It means the heavens are not silent to anyone. And it means the teacher of Scripture should approach every listener, believer or skeptic, with the humility of one who also needs the truth daily uncovered. Aquinas would recognize that posture immediately; it is the posture of a student, and he called theology sacred doctrine precisely because its subject matter exceeds its students.
Creation and the Knowledge of God in Aquinas's Reading
Psalm 19:1 says the heavens declare the glory of God, and the expanse shows his handiwork. Aquinas heard that as a second witness to Romans 1: creation is not a mute backdrop but a proclamation. He did not think this meant everyone becomes a theologian by looking at stars. He thought it meant no one looks at stars without standing before a claim. The created order is a kind of speech, and speech addressed to someone requires a response. Ignoring it is not neutral; it is a refusal to answer.
He also insisted that creation is not God. The Creator and the creature are not the same kind of thing, and the difference is not merely quantitative. This is why Romans 1's exchange is so serious: idolatry confuses the gift with the giver. Aquinas's metaphysics served his worship here. If God is being itself, not a very large being among beings, then every image that claims to capture him is a lie, and every concept that claims to contain him is a signpost, not a destination. The most precise theology ends in silence, because the reality exceeds the words.
Yet he did not conclude that words are useless. He wrote millions of them, and he did so because the God who exceeds our concepts has nevertheless made himself known through creatures, through Scripture, and supremely through the Word made flesh. Natural theology is possible because God chose to be knowable through what he made. It is limited because what he made is not him. It is necessary because Paul says the alternative is suppressing the truth and exchanging glory for images.
This is the balance the passage demands, and it is the balance Aquinas kept. Creation reveals. Sin suppresses. Grace restores. Revelation clarifies. The result is not a rationalist who needs no gospel, nor a fideist who despises reason, but a theologian on his knees, using every tool God gives, and finally trusting the God who gives them. That is a portrait worth studying, and it begins with reading Romans 1 as Paul wrote it.
Biblical fidelity check
Romans 1:18-23 establishes that God's wrath is revealed against suppression of truth, that what can be known of God is plain to people because God made it plain, that his invisible attributes are perceived through created things, and that those who reject him are without excuse. It also establishes that the human response was not glorifying God, not giving thanks, futile reasoning, a darkened heart, and idolatrous exchange. It does not establish that natural reason can discover the Trinity, the incarnation, or justification by faith. It does not establish that everyone who has never heard the gospel is saved. It does not establish that philosophical arguments produce conversion.
A common misreading treats the passage as a proof that sincere seekers everywhere can find God by reason if they try hard enough. That reading ignores Paul's own conclusion: the nations did not glorify him, and their reasoning became vain. The passage is an indictment before it is an invitation, and it ends in darkness to make the gospel shine. A second misreading, common among critics of Aquinas, treats him as if he replaced the cross with Aristotle. But Aquinas wrote commentaries on Paul, preached on the cross, and insisted that grace is necessary for salvation. Faithful Christians differ over how much weight to give natural theology, and that disagreement should be stated honestly, but neither misreading is faithful to the text or to Thomas.
Other passages that speak to Romans 1:18-23
Several related studies help fill out the picture. Acts 17:22-31 shows Paul addressing philosophers on their own ground before calling them to repentance, which many read as a companion to Romans 1. First Corinthians 1:18-25 presses the point that the cross is foolishness to the dying and wisdom to the saved, a theme that qualifies any confidence in human reasoning. Colossians 2:8-10 warns against philosophy that is not after Christ, which is not a rejection of all thought but a boundary around it. Proverbs 9:10 grounds understanding in the fear of Yahweh, and Psalm 19:1-4 joins creation's speech to the argument Paul makes. For broader context, see What Does 1 Corinthians 1:10 Mean? Context, Theology, and Application, What Does 1 Corinthians 1:9 Mean? Context, Theology, and Application, 1 Corinthians 1: Called, United, and Boasting in the Lord, and 1 Corinthians 10: Warnings and Freedom.
Frequently asked questions
Did Aquinas believe reason could save a person?
No. Aquinas held that reason can establish that God exists and that certain truths about him follow from creation, but he denied that reason can reach the saving knowledge of God as Father, Son, and Spirit, or grasp the gospel of the crucified and risen Christ. Those come by revelation and are received through faith, which he described as a gift of grace. The knowledge Romans 1 describes leaves people without excuse; it does not reconcile them to God. Aquinas's theology of grace stands alongside his natural theology, not beneath it.
Does Romans 1 teach that everyone already knows God?
Paul says that what can be known of God is plainly seen in creation, and that people knew God but did not honor him as God or give thanks. That is not the same as saying everyone consciously affirms God's existence. It means creation is a genuine disclosure, and the failure to respond is culpable suppression rather than honest ignorance. Aquinas read it this way: the knowledge is real but darkened and held down by unrighteousness, so the problem is moral and cognitive at once, and the remedy must be grace rather than more information.
How should Christians use natural theology today?
Natural theology can help clear away objections, expose the inconsistency of treating the universe as self-explanatory, and show that faith is not irrational. It cannot produce repentance or love for God. Christians differ over how far natural arguments should be pressed and whether they are essential to apologetics, and that disagreement is legitimate. Aquinas would have us hold both convictions: use every honest argument, and trust the Spirit to do what arguments cannot. The goal is not to win a debate but to see a person turn to the living God.
