The mountains; which he mentions as the most fixed and stable part of the earth. Or ever thou hadst formed the earth and the world, i.e. from eternity; which is frequently described in this manner, as Proverbs 8:25,26 Joh 17:24 Ephesians 1:4, because there was nothing before the creation of the world but eternity. And thus the words here following do explain it. And this eternity of God is here mentioned, partly that men by the contemplation thereof might be wrought to a deeper sense of their own frailty and nothingness, which is the foundation of humility and of all true piety, and to a greater reverence and admiration of the Divine Majesty; and partly for the comfort of God's people, who notwithstanding all their present miseries have a sure and everlasting refuge and portion. Thou art God; or, thou art the strong God. Thou hast thy power and all thy perfections, not by degrees, as men have theirs, but from all eternity. Or, thou art or wast, O God.
Related Commentaries of Psalms 90:2
Psalms 90:2
2 Before the mountains were brought forth, or ever thou hadst formed the earth and the world, even from everlasting to everlasting, thou art God.