Charles H. Spurgeon on Psalms 90:2

Before the mountains were brought forth. Before those elder giants had struggled forth from nature's womb, as her dread firstborn, the Lord was glorious and self sufficient. Mountains to him, though hoar with the snows of ages, are but new born babes, young things whose birth was but yesterday, mere novelties of an hour. Or ever thou hadst formed the earth and the world. Here too the allusion is to a birth. Earth was born but the other day, and her solid land was delivered from the flood but a short while ago. Even from everlasting to everlasting, thou art God, or, "thou art, O God." God was, when nothing else was. He was God when the earth was not a world but a chaos, when mountains were not upheaved, and the generation of the heavens and the earth had not commenced. In this Eternal One there is a safe abode for the successive generations of men. If God himself were of yesterday, he would not be a suitable refuge for mortal men; if he could change and cease to be God he would be but an uncertain dwelling place for his people. The eternal existence of God is here mentioned to set forth, by contrast, the brevity of human life.