John Calvin Commentary Genesis 19:29

"And it came to pass, when God destroyed the cities of the Plain, that God remembered Abraham, and sent Lot out of the midst of the overthrow, when he overthrew the cities in which Lot dwelt." — Genesis 19:29 (ASV)

God remembered Abraham. Although Moses does not assert that the deliverance of Abraham’s nephew was made known to him, yet since he says that Lot was saved from destruction for Abraham’s sake, it is probable that he was not deprived of that consolation which he most needed, and that he was conscious of the benefit for which it was fitting for him to give thanks.

If it seems absurd to anyone that the holy man Lot should be spared for the sake of another, as if the Lord had no regard for Lot's own piety, I answer that these two things agree well with each other: that the Lord, since he is accustomed to aid his own people, cared for Lot, whom he had chosen and whom he governed by his Spirit; and yet, at the same time, he would show in the preservation of Lot's life how greatly he loved Abraham, to whom he not only granted personal protection but also the deliverance of others.

It is right to observe, however, that what the Lord does gratuitously—induced by no other cause than his own goodness—is ascribed to the piety or the prayers of people for this reason: that we may be encouraged to worship God and to pray to him.

We have seen a little earlier how merciful God proved himself to be in preserving Lot; and truly, Lot would not have perished even if he had not been Abraham's nephew. Yet Moses says it was a favor granted to Abraham that Lot was not consumed in the same destruction with Sodom.

But if the Lord extended the favor which he had granted to his servant to the nephew also, who was now like a stranger from his family, how much more confidently should everyone among the faithful expect that the same grace will by no means be lacking to his own household?

And, if the Lord, when he favors us, also embraces others connected with us for our sake, how much more will he have regard for us? In saying that Lot lived in those cities, the figure synecdoche (which puts the whole for a part) is used. It is expressly employed to make the miracle more remarkable, because it happened only by the singular providence of God that when five cities were destroyed, a single person escaped.