Matthew Poole and continuators on 1 Samuel 20:15

15 But also thou shalt not cut off thy kindness from my house for ever: no not when the LORD hath cut off the enemies of David, every one from the face of the earth .

He saith not, the kindness of the Lord, as before, because the Covenant between them seems to have been onely Personal, and not comprehending their Posterity. And therefore as Ionathan speaks confidently of his own Preservation by vertue of that Covenant; so he here lays this additional Obligation upon David, That he would extend this kindness to all his Progeny.

Which he will certainly do without exception of Saul my Father, and those of his Children who have joyned, or shall joyn with him in his Hostilities and Cruelties against David. And by this word, Enemies, he implies the reasonableness of his request, because Ionathan was none of that number, and therefore not to be treated as such.

Marginal references: 2 Sam. 9. 3.