Clarke's Bible Commentary - 1 Samuel 18:1
Verse 1. When he had made an end of speaking] These first five verses are omitted by the Septuagint. See the notes on the preceding chapter. Jonathan loved him as his own soul] The most intimate friendship subsisted between them; and they loved each other with pure hearts fervently. No love was lost between them; each was worthy of the other.
They had a friendship which could not be affected with changes or chances, and which exemplified all that the ancients have said on the subject; thn filian isothta einai, kai mian yuchn, ton filon eteron auton; "Friendship produces an entire sameness; it is one soul in two bodies: a friend is another self."
John Gill's Bible Commentary
Ver. 1. And it came to pass, when he had made an end of speaking unto Saul , etc.] In answer to his questions about his descent and family, and doubtless more things were talked of than are recorded: that the soul of Jonathan was knit with the soul of David : he won his heart, made a conquest of his affections, these went out towards him, and cleaved unto him; such were the comeliness of his person, his graceful mien and deportment, his freedom and fluency of expression, his courage and undauntedness, joined with prudence, modesty, and integrity, that they strongly attached him to him: and Jonathan loved him as his own soul ; not only according to the excellency of David’s soul, and the greatness of it, as that deserved respect and love, as Abarbinel suggests, but he loved him as he loved himself.
There was a similarity in their persons, in their age, in the dispositions of their minds, in their wisdom, courage, modesty, faithfulness, and openness of soul, that attracted them to each other, that they became as another self; as one soul, as Aristotle speaks of true friends: instances of very cordial friendship are given by Plutarch f385 , as in Theseus and Pirithous, Achilles and Patroclus, Orestes and Pylades, Pythias and Damon, Epaminondas and Pelopidas; but none equal to this.
Matthew Henry Commentary
Verses 1-5 - The friendship of David and Jonathan was the effect of Divine grace which produces in true believers one heart and one soul, and cause them to love each other. This union of souls is from partaking in the Spirit of Christ. Where God unites hearts, carnal matters are too wea to separate them. Those who love Christ as their own souls, will be willing to join themselves to him in an everlasting covenant. It wa certainly a great proof of the power of God's grace in David, that he was able to bear all this respect and honour, without being lifted u above measure.
Original Hebrew
ויהי 1961 ככלתו 3615 לדבר 1696 אל 413 שׁאול 7586 ונפשׁ 5315 יהונתן 3083 נקשׁרה 7194 בנפשׁ 5315 דוד 1732 ויאהבו 157 יהונתן 3083 כנפשׁו׃ 5315
