John Calvin Commentary Deuteronomy 2:19

"and when thou comest nigh over against the children of Ammon, vex them not, nor contend with them; for I will not give thee of the land of the children of Ammon for a possession; because I have given it unto the children of Lot for a possession." — Deuteronomy 2:19 (ASV)

And when you come near, over against the children of Ammon. God now makes provision concerning the Ammonites, since their situation was the same as that of the Moabites, because they were descended from Lot's two daughters.

It might, indeed, seem surprising that, since the memory of their origin was detestable, these two nations should have been so dear to God. Ammon and Moab had been born of an incestuous connection. It was, therefore, more reasonable that this tragic circumstance should have been buried by their destruction, rather than that they should have been distinguished by God’s favor from the common lot of other nations, as if their nobility made them superior to others.

But let us learn from this that since God’s judgments, like a deep abyss, are beyond our comprehension, they should be regarded with reverence. Lot’s distinguished piety is expressly declared. The disgraceful crime which he committed when drunk, God was pleased to mark with perpetual infamy, yet in such a way as to still impress upon it some signs of His mercy, although this was done especially for Abraham's sake.

It is unquestionable, however, that God commends Lot's descendants to the Israelites on this basis: that they might more willingly show kindness toward them and refrain from all injury, when they had to deal with two nations whom they saw were cared for by God Himself, for the sake of their common relationship to Abraham.

Furthermore, by the same argument by which he had previously proved that both Edomites and Moabites, relying on God’s help, had occupied the lands they ruled, he now establishes that the land the Ammonites possessed had been granted to them by God, namely, because in their conquest and overthrow of the giants they had surpassed the limits of human bravery, and thus God had given proof of His special and unusual favor toward them. For not even by the ordinary course of nature could two men increase to such a great multitude.

Now, although in Hebrew the Cappadocians are called Caphthorim,¹²⁷ we do not know whether the giants, whose country the Ammonites took possession of, originated from them.

But, if this is accepted, they had a long journey, attended by many dangers, after they left their country. Furthermore, since they must have passed through rich and fertile regions, it is strange that they should have penetrated to those mountains.

It might, however, be the case that, making raids as robbers, they found no quiet resting place anywhere until a less cultivated region presented itself.

¹²⁷ Bochart remarks that all ancient writers are unanimous in supposing Caphthor to be Cappadocia, and the Caphthorim Cappadocians; but he assigns to them that part of Cappadocia only which bordered on Colchis. Phaleg. Book 4, chap. 32:— See Book 4, chap. 32:— See C. on . on Jeremiah 47:4,, C. Soc. Edit., vol. 4, p 614..