Swear again — Heb. and Jonathan added or proceeded to make David 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. 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.