Paul sets anxious fretting and prayer as opposing responses, then promises not a changed situation but God's own peace standing guard over heart and thoughts in Christ Jesus.

Paul does not tell the anxious to calm themselves down. He points them to specific, thankful prayer, and promises that God's own peace will stand guard over heart and thoughts in Christ Jesus.

Paul does not tell the anxious Philippians to calm themselves down. He tells them to bring named requests to God with thanksgiving, and he promises that God's own peace will stand guard over their hearts and thoughts.

Paul does not tell anxious people to try harder. He redirects the anxious mind toward God in prayer and thanksgiving, and points to a peace that stands guard over the heart rather than a peace that depends on circumstances.