Matthew Poole and continuators on Genesis 21:24

24 And Abraham said, I will swear .

Quest. How could Abraham lawfully swear this, when Canaan was given by God to him and his seed for ever? Answ. Neither Abraham nor his seed had any present and actual right to the possession of the Land, but onely the promise of a right in it, and possession of it after some hundreds of years, and therefore he gave away none of his right by this Oath. For this Oath did only oblige Abraham and not his Posterity, and Abimelech extended that obligation no further than to his Sons Son.