Genesis 15:16

But in the fourth generation, they shall return here. Kohath entered Egypt with his father Levi, whose son was Amram, whose son was Aaron, whose son was Eleazar, who was the fourth from Kohath. And he went out from Egypt with his father Aaron, and when he died in the wilderness, he himself entered the Promised Land.

(Verse 16) But in the fourth generation they will return here. There is no doubt that these will be the ones who are descended from Abraham. It is asked how it is written in Exodus: In the fifth generation the children of Israel went forth from the land of Egypt (Exodus 15:18). On this chapter, we have published a small volume.

The history of the Jews, who went down into Egypt and came out from Egypt, seems to accord with this. The years they spent there were 430, but not all of them lived a hundred years and more, as did Moses and Joshua, so that the time of the fourth generation would be appropriate in this context. So let us search rather for a mystical sense. In fact, the number four adapts well to all numbers, and it is in a certain sense the root and base of the decimal. It also represents the midpoint of the number seven. In fact, the ninety-third psalm is entitled "fourth day of the week" because this number is the intermediary between the first three and those that follow. In fact, three days precede it: the first, the second and the third; and three follow: the fifth, the sixth, the seventh. One who sings this psalm is proceeding through the life of this world, so to speak, in accordance with aptly placed numbers, like a quadrangle stable and perfect. In four books the Gospel is complete and perfect. There are four mystical animals; and there are also four parts of the world, from which the assembled children of the church have propagated the most holy kingdom of Christ, coming from east and west and north and south. The holy church, therefore, has arisen with four sides. The decade too derives from this number. For if you total up the numbers from one to four you will have the number ten. Count one, add two to this: this makes three. Add three to three, this makes six. And to six add four, and this makes ten. Four then generates the decade, and the decade includes all numbers. Four is also the number of ages of a man: childhood, adolescence, virility and maturity. He rises gradually, and his wisdom is consolidated. Thus the fullness of wisdom comes, considering the ages, in fourth place. For this reason even if one has formerly been subjected to the king of Egypt, nevertheless with the age of maturity he is freed from his power and acknowledges his duty to follow the law. Then the sea of this life opens up to him.