1 Samuel 20:17

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

Jonathan loved David deeply, as he loved his own soul and himself, and that love was deep and enduring. Their love was expressed in a covenant to be united as brothers, with Jonathan giving David his robe and weapons. It was sealed by a solemn oath sworn again in the name of the Lord that the Lord would be between them and between their seed forever.

Jonathan believed in David's innocence and interceded with Saul for him even at risk to his own life and throne. Through that sacred bond God used Jonathan to preserve David's life when Saul tried to kill him. David trusted that love and appealed to Jonathan when Saul sought his life. When Saul's rage made David's flight certain, they met at the appointed field, fell on each other's neck, wept bitterly, and parted in peace, with Jonathan returning to Gibeah and David going into exile under the shadow of Saul's hatred.

The covenant included David's promise that when he should have rest from his enemies he would show kindness to the house of Saul. In prosperity David remembered it by asking if any were left of the house of Saul that he might show kindness for Jonathan's sake. He found Jonathan's son Mephibosheth, lame from childhood when his nurse let him fall while fleeing at Saul's defeat by the Philistines at Jezreel. David summoned him to court, restored Saul's private possessions for the support of his household, and made him a constant guest sitting daily at the royal table. Mephibosheth had been led by David's enemies to view David as a usurper, but David's generous reception and continued kindness won his heart, and like his father Jonathan he became strongly attached to David, feeling his interest was one with that of the king whom God had chosen.