Charles Ellicott Commentary 1 Samuel 18:3

"Then Jonathan and David made a covenant, because he loved him as his own soul." — 1 Samuel 18:3 (ASV)

Made a covenant. The son of the first Hebrew king recognized in David a kindred spirit. They were one in their God, in their faith, in their devotion to the Divine will. Jonathan recognized in the young shepherd, who unarmed went out alone to meet the mighty Philistine warrior, the same spirit of sublime faith in the Invisible King. This same spirit had inspired Jonathan himself in days long ago to go out alone with his armor-bearer to attack and capture the Philistine stronghold. It was then he spoke those memorable words that enable us to understand his character: It may be that the Lord will work for us: for there is no restraint to the Lord to save by many or by few (1 Samuel 14:6).

The great friendship, which has been the admiration of subsequent generations, began with the strong faith in the Eternal common to the two friends. Throughout its duration, the link that united them was an intense desire to do the will of Him who, as true Hebrew patriots, they felt loved Israel; and when the friends parted for the last time in the wilderness of Ziph, we are told how the elder (Jonathan) strengthened the younger (David’s) hand in God (1 Samuel 23:16).