Genesis 21:23

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. Abraham was still living in the land of the Philistines, and the latter were unable to deny that a special blessing of God rested upon Abraham. This fact finally prompted Abimelech to propose a covenant between himself and Abraham, in order to secure the friendship of this man for himself and his children. The chief condition was that there was to be no false or double dealing, and Abimelech reminds Abraham of the fact that he had shown merciful kindness to him at the time when he lived in Gerar, Genesis 20:15. His appeal was to Abraham's generosity, gratitude, and faithfulness.