The Cup of the New Covenant: Matthew 26:26–28
Jesus does not describe an oath ritual at the Last Supper. He takes bread and a cup and announces a covenant sealed by his own blood, given for the forgiveness of sins. The biblical meaning of a blood oath belongs to covenant, not to private vows.
John 13:23: The Disciple Whom Jesus Loved
John 13:23 does not tell us why Jesus loved John. It tells us that being loved is how this disciple is known, and that his nearness at the table became the place from which Peter's question was asked.
Why Jesus Washed the Disciples' Feet
Jesus washed his disciples' feet not to establish a ritual but to show his own people what lowly, self-giving love looks like from the inside. The blessing he names belongs to those who actually do it.
Judas Iscariot's Father: Simon Iscariot in John 13
John's account of the Last Supper names Judas Iscariot's father plainly: Jesus calls him the son of Simon Iscariot. The detail arrives at the moment of the betrayal announcement, not as a footnote.