1 Samuel 20:16,17

So Jonathan made a covenant The covenant which before was personal, he now extends to the whole house of David, expecting a reciprocal enlargement of it on David's side, which doubtless he obtained. At the hand of David's enemies If either I, or any of my house, shall prove enemies to David or to his house, let the Lord, the witness of this covenant, severely punish the violators of it. Jonathan caused David to swear again Hebrew, and Jonathan added or proceeded to swear; that is, having himself sworn to David, or adjured David, in the foregoing verse, he here requires David's oath to him, by way of restipulation or confirmation. For he loved him, &c. The greatness of his love to him induced him to use every means in his power to secure David's friendship to himself and his posterity, and to ensure the inviolable observance of this covenant through all their generations.