1 Samuel 18:3 - Joseph Benson’s Commentary on the Old and New Testaments

Jonathan and David made a covenant Solemnly entered into an agreement of perpetual friendship. Because he loved him, &c. Or rather, as Le Clerc renders it, so that each loved the other as his own soul. For it cannot be supposed but that David loved Jonathan as well as Jonathan loved him. Their covenant seems to have implied an engagement for mutual assistance and defence, even until death, and kindness to the posterity of each other after either of them was dead. This was wisely ordered by the providence of God, who, by this means, preserved David in that sharp persecution which shortly after rose against him at court.