Charles Spurgeon Commentary 1 Samuel 18:1

"And it came to pass, when he had made an end of speaking unto Saul, that the soul of Jonathan was knit with the soul of David, and Jonathan loved him as his own soul." — 1 Samuel 18:1 (ASV)

And it came to pass, when he had made an end of speaking unto Saul, that the soul of Jonathan was knit with the soul of David, and Jonathan loved him as his own soul.

Jonathan, the brave young soldier who had himself done great exploits, naturally admired the youthful warrior who had slain the Philistine giant, and also admired the modesty of his speech when he returned with the head of Goliath in his hand: The soul of Jonathan was knit with the soul of David, and Jonathan loved him as his own soul.