Chapter 18 — Part II: The Sacraments — The Holy Eucharist
Section 32. Should the authority of John the Evangelist, who says that all this was done before the feast of the Passover, be objected to, the argument is one of easy solution. For by the day before the pasch John understands the same day which the other Evangelists designate as the first day of unleavened bread. He wished particularly to mark the natural day, which commences at sunrise; whereas they wanted to point out that our Lord celebrated the Pasch on Thursday evening just when the days of the unleavened bread were beginning. Hence St. Chrysostom also understands the first day of unleavened bread to be the day on the evening of which unleavened bread was to be eaten.