Or HaChaim on Deuteronomy 2:11/אור החיים על דברים ב׳:י״א

1 רפאים יחשבו, these are accounted as Rephaim, etc. Why did the Torah consider it necessary to tell us that these people were considered Rephaim (as of gigantic proportions)? I believe that the fact that amongst the ten nations whose lands G'd had promised to give to Abraham's descendants in Genesis 15,20 the Rephaim are mentioned, the Torah wanted to inform us that Or which G'd gave to the descendants of Lot as an inheritance was identical with the Rephaim mentioned by G'd in Genesis. This is why Moses added: "the Eymim used to live there in previous times;" the "previous times" mentioned by Moses was the period prior to G'd's promise to Abraham, at the covenant between the pieces in Genesis chapter 15. Moses reminded the people that the merit of Abraham will stand by them.