Genesis 21:23

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.