“If therefore it could be that the Lord’s day should always happen on the fifteenth day of the first month, that is, on the fifteenth moon, we might always celebrate the Passover at one and the same time with the ancient people of God, though the nature of the mystery be different, as we do it with one and the same faith. But inasmuch as the day of the week does not keep pace exactly with the moon, the Apostolic tradition, which was preached at Rome by the blessed Peter, and confirmed at Alexandria by Mark the Evangelist,(963) his interpreter, appointed that when the first month was come, and in it the evening of the fourteenth day, we should also wait for the Lord’s day, between the fifteenth and the one-and-twentieth day of the same month. For on whichever of those days it shall fall, Easter will be rightly kept on the same; seeing that it is one of those seven days on which the feast of unleavened bread is commanded to be kept. Thus it comes to pass that our Easter never falls either before or after the third week of the first month, but has for its observance either the whole of it, to wit, the seven days of unleavened bread appointed by the law, or at least some of them. For though it comprises but one of them, that is, the seventh, which the Scripture so highly commends, saying,(964) ‘But the seventh day shall be a more holy convocation, ye shall do no servile work therein,’ none can lay it to our charge, that we do not rightly keep Easter Sunday, which we received from the Gospel, in the third week of the first month, as the Law prescribes.