'Swear' in the Bible

And Jonathan caused David to swear again, because he loved him: for he loved him as he loved his own soul.

Swear now therefore unto me by the LORD, 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 company? And he said, Swear unto me by God, that thou wilt neither kill me, nor deliver me into the hands of my master, and I will bring thee down to this company.