And in the fourth generation they shall come hither again,.... The seed of Abram were in the land of Canaan before their descent into Egypt; and it is here predicted and promised, that they should come thither again, as they did, in the fourth generation of those that descended thither; for Moses and Aaron were the fourth from Levi, or Eleazar from Kohath, and Caleb from Judah; or rather this was in the fourth age or century from the birth of Isaac, when the four hundred were up before mentioned, men living at that time about an hundred years: Grotius interprets this of the fourth generation of the Amorites, because of what follows:for the iniquity of the Amorites [is] not yet full; and therefore as yet would not be turned out of the land, and the seed of Abram could not till then inherit it: wicked people have a measure of iniquity to fill up, which is known of God; some are longer, some are quicker in filling it up, during which time God waits patiently and bears with them; but, when it is completed, he stays no longer, but takes vengeance on them, Mt 23:32.
The Amorites were only one of the nations of the Canaanites, but were a very strong and powerful one, and are put for them all, and are the rather mentioned, because Abram at this time dwelt among them; and it seems as if there were some good men among them, such as the confederates of Abram might be, and they were not arrived to that depth of wickedness they afterwards would and did, and which brought on their ruin, and so made way for the posterity of Abram to inherit their land.