The fewest To wit, at that time, when God first declared his choice of you for his peculiar people, which was done to Abraham. For Abraham had but one son concerned in this choice and covenant, namely, Isaac, and that was not till he was in his hundredth year; and Isaac was sixty years old ere he had a child, and then had only two children; and though Jacob had twelve sons, yet it was a long time before they made any considerable increase. Nor do we read of any great multiplication of them until after Joseph's death. The Lord loved you It was his free choice, without any cause or motive on your part.
Related Commentaries of Deuteronomy 7:7
Deuteronomy 7:7-8
7 The LORD did not set his love upon you, nor choose you, because ye were more in number than any people; for ye were the fewest of all people:
8 But because the LORD loved you, and because he would keep the oath which he had sworn unto your fathers, hath the LORD brought you out with a mighty hand, and redeemed you out of the house of bondmen, from the hand of Pharaoh king of Egypt.