'Swear' in the Bible

And Jonathan caused David to swear again, by the love he had for him, for he loved him as he loved his own soul.

Swear now therefore to me by Jehovah, that thou wilt not cut off my seed after me, and that thou wilt not destroy my name out of my father's house.

And David said to him, Canst thou bring me down to this troop? And he said, Swear to me by God, that thou wilt neither put me to death nor deliver me up into the hand of my master, and I will bring thee down to this troop.