God was not declared to be a god, as has been the case with many human beings, virtually all of whom are now dead and gone. In their regard a glaring question must be asked, "how does a supposed god die?" The same point can be made, in principle, pertaining to the countless idols that have been worshipped throughout the millennia. What happened to them, where are they today?
By contrast the apostle Paul referred to God's "eternal power and Godhead" (Rom. 1:19-20). God's plan for man's salvation, brought to this earth by Jesus Christ, was according to His "eternal purpose" (Eph. 3:9-11). In His omniscience God knew, before He ever created mankind, that humanity would fall through sin and consequently need forgiveness and redemption. As a result, God designed a plan for man's salvation from "before time began" (Tit. 1:2).
It's difficult for us, as mere human beings, to fully wrap our minds around the concept of God being eternal. We can imagine time without end, but we have real difficulty grasping the idea of time without beginning. Yet that's exactly the meaning behind the phrase "from everlasting to everlasting." This is but another aspect of His unique nature that identifies Him as truly being God!
Undoubtedly, we will more readily understand when we stand in His very presence in Heaven and begin our eternity with our eternal Father. Until then, we can be thankful that we serve the God of eternity. How aptly the psalmist put it: "Blessed be the Lord God of Israel from everlasting to everlasting! And let all the people say, 'Amen!' Praise the Lord!" (Ps. 106:48).