Timothy George on "The Eternity of God":
.... The Bible says that the number of God’s years is “unsearchable” (Job 36:26). God is the one “who lives forever” (Isa 57:15). He is therefore utterly distinct from everything that exists outside of himself; he is before and after, above and beneath, incomparable to all creaturely realities, including the heavens and the earth. As the psalmist says, “They will perish, but thou remainest, and they all will become old as a garment, and as a mantel thou wilt roll them up; as a garment they will also be changed. But thou art the same, and thy years will not come to an end” (Ps 102:26, as quoted in Heb 1:11–12). “Before Abraham was,” Jesus said, “I AM” (John 8:58). The eternity of the Son was a major concern in the development of the orthodox doctrine of the Trinity in the early church. What Athanasius and the other Nicene theologians (including the Cappadocians) said about the Logos is no less true of the Father and the Holy Spirit: Before he was, there was not.
In books 10 and 11 of the Confessions, Augustine takes up the mystery of time and eternity. .... This is what he said: It makes sense to ask what God was doing before he made the world if, and only if, both God and the world are separate items within the same temporal continuum. But they are not. God’s years, unlike ours, do not come and go. They are succeeded by no yesterday, and they give way to no tomorrow. “It is not in time that you precede all times, O Lord. You precede all past times in the sublimity of an ever-present reality. You have made all times and are before all times.” ....
God’s changelessness does not mean that he is a static being, incapable of being affected by anything outside of himself, a deity locked forever in the prison of his own aseity. Such a concept might describe Aristotle’s Unmoved Mover, but it falls far short of the God of biblical revelation, the God who is actively involved with the world he has made and who entered directly into that world as a squirming baby in a messy manger.
God’s immutability refers instead to his constancy and faithfulness. “I am the Lord, I change not; therefore ye sons of Jacob are not consumed” (Mal 3:6). “Every good endowment and every perfect gift is from above, coming down from the Father of lights with whom there is no variation or shadow due to change” (James 1:17). The God of the Bible is not only the Creator of time but also the Lord of time. Unlike human beings who are creatures of a day, God is the one whose steadfast love endures forever, whose faithfulness is to all generations: “The Lord reigns; he is robed in majesty; the Lord is robed, he is girded with strength. Yea, the world is established; it shall never be moved; thy throne is established from of old; thou art from everlasting” (Ps 93:1–2). .... [more]