Now therefore swear unto me here by God that thou wilt not deal falsely with me, nor with my son, nor with my son's son: but according to the kindness that I have done unto thee, thou shalt do unto me, and to the land wherein thou hast sojourned. Now therefore swear unto me - The oath on such occasions probably meant no more than the mutual promise of both the parties, when they slew an animal, poured out the blood as a sacrifice to God, and then passed between the pieces. See this ceremony, Genesis 15:18 (note), and on Genesis 15 (note).
According to the kindness that I have done - The simple claims of justice were alone set up among virtuous people in those ancient times, which constitute the basis of the famous lex talionis, or law of like for like, kind office for kind office, and breach for breach.