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.
Genesis 12 to 26 records God's providential dealings with the family of Abraham as the chosen progenitor of the promised Seed, belonging to the history of beginnings and to the story of God's dealing with the Seed. In Genesis 21 Isaac stands as the miraculous child of promise through whom the promised Seed would come, rather than through Ishmael. The verse belongs to the account of Abraham's separation from Abimelech, king of the Philistines.
Abimelech sought the covenant because he recognized that God was with Abraham, which shows that knowledge of the Lord was known beyond Abraham's family. Abimelech asked Abraham to swear by God to deal honestly and faithfully with him, with his son and his grandson, and with the land where Abraham had sojourned, in return for the kindness Abimelech had shown him and for his continued presence in the land. By a different reading held by fewer, it was Abraham who asked Abimelech to deal faithfully with him, his descendants, and the land where he had lived as a sojourner, in return for the kindness Abraham had shown.
Covenant here means a mutual agreement in which Abraham and Abimelech made mutual promises about how they would treat one another, including not to deal falsely and to show reciprocal kindness. The agreement concerned the well at Beer-sheba, whose name means well of the oath and commemorated their agreement. Abraham first made the covenant of friendship confirmed by an oath and then raised the wrong done by Abimelech's servants concerning a well of water without breaking friendship, showing that meekness allows a wrong to be addressed and disagreements to be fairly discussed and settled while preserving friendship.
The covenant was respected while Abraham lived, but after his death the Philistines stopped up the wells he had dug. The verse is connected with the everlasting life of the redeemed, pictured as a day with no setting sun or following night.