Matthew Poole and continuators on Psalms 103:17

17 But the mercy of the LORD is from everlasting to everlasting upon them that fear him : and his righteousness unto childrens children:

But though we quickly decay and perish, yet Gods mercy to us doth not die with us, but as it was from Eternity exercised in gracious purposes, so it will be continued unto eternity in that future and endless life.

See before on v. 11.

Either his faithfulness: or (that this branch may answer to the former) his mercy or benignity: this word being frequently used in both these sences, as hath been proved before. But it is here called righteousness, to intimate that Gods kindness to the posterity of his people is not onely an act of his goodness but also a discharge of his obligation under which he put himself to them as elsewhere, so Exod. 20. 6. to which this place seems to relate. Hence it is called mercy to Abraham, and truth to Iacob, Mic. 7. 20.