The synod of 664 met to decide which of two methods of calculating Easter the Northumbrian church would keep. The problem was practical before it was theological: King Oswiu had been trained in the Ionan tradition and his queen Eanflaed in the Roman, so in some years the king was celebrating the resurrection while the queen was still fasting through Lent, and the court kept two calendars.
Colman, bishop of Lindisfarne, argued for the Ionan reckoning on the authority of Columba and, behind him, of John the Evangelist. Wilfrid argued for the Roman on the authority of Peter and of the practice of the wider church, and, as Bede tells it, closed by pointing out that Peter holds the keys of heaven. Oswiu asked Colman whether that was so, was told it was, and decided for Rome.
Colman resigned and withdrew to Iona and then to Ireland with those who would not accept the ruling. Everything known about the synod comes from Bede, writing sixty years later and firmly on the winning side, and he presents it as the moment the English church joined the universal one; the form of the tonsure and other Ionan customs were at issue as well as the date. What was not at stake was any point of doctrine, which is worth saying plainly, because the synod is often described as though it had been.