Augustine of Hippo
Catena Aurea · Lukasevangelium 4
And Jesus being full of the Holy Ghost returned from Jordan, and was led by the Spirit into the wilderness, Being forty days tempted of the devil. And in those days he did eat nothing: and when they were ended, he afterward hungered. And the devil said unto him, If thou be the Son of God, command this stone that it be made bread. And Jesus answered him, saying, It is written, That man shall not live by bread alone, but by every word of God.
(de Con. Ev. lib. ii. c. 4.) Now that number is a sacrament of our time and labour, in which under Christ’s discipline we contend against the devil, for it signifies our temporal life. For the seasons of the year run in courses of four, but forty contains four tens. Again, those ten are completed by the number one successively advancing up to four. This plainly shews that the fast of forty days, i. e. the humiliation of the soul, the Law and the Prophets have consecrated by Moses and Elias, the Gospel by the fast of our Lord Himself.