Heb. And Jonathan added or proceeded to make David swear, i.e. 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. Because he loved him; because he had a true friendship for David, he desired that the covenant might be inviolably observed through all their generations.
Related Commentaries of 1 Samuel 20:17
1 Samuel 20:17
17 And Jonathan caused David to swear again, because he loved him: for he loved him as he loved his own soul.