The concept of eternity and how is God eternal can be confusing to understand. Two questions are often asked:

Does it mean God lives forever throughout time and exists at every point in time?

Does it mean that God is timeless and lives outside of time? Is God unaffected by time?

1. Does God exist within or outside of time?

Then God said, "Let there be light"; and there was light. And God saw that the light was good; and God separated the light from the darkness. And God called the light day, and the darkness He called night. And there was evening and there was morning, one day. (Gen 1:3-5, LSB)

Then God said, "Let there be lights in the expanse of the heavens to separate the day from the night, and let them be for signs and for seasons and for days and years; and let them be for lights in the expanse of the heavens to give light on the earth"; and it was so. (Gen 1:14-15, LSB)

Now to Him who is able to keep you from stumbling, and to make you stand in the presence of His glory blameless with great joy, to the only God our Savior, through Jesus Christ our Lord, be glory, majesty, might, and authority, before all time and now and forever. Amen. (Jude 1:24-25, LSB)

2. When Jesus was born, did He exist only within time?

The book of the genealogy of Jesus Christ, the son of David, the son of Abraham:
Abraham was the father of Isaac,
and Isaac was the father of Jacob,
and Jacob was the father of Judah and his brothers. (Matt 1:1-2, LSB)

Therefore all the generations from Abraham to David are fourteen generations; and from David to the deportation to Babylon, fourteen generations; and from the deportation to Babylon to the Christ, fourteen generations. (Matt 1:17, LSB)

Then God said, "Let Us make man in Our image, according to Our likeness, so that they will have dominion over the fish of the sea and over the birds of the sky and over the cattle and over all the earth and over every creeping thing that creeps on the earth." (Gen 1:26, LSB)

Who is the image of the invisible God, the firstborn of all creation. For in Him all things were created, both in the heavens and on earth, visible and invisible, whether thrones or dominions or rulers or authorities⁠—all things have been created through Him and for Him. (Col 1:15-16, LSB)

3. What do you observe at the end of human history and your understanding of time?

Then I saw a new heaven and a new earth; for the first heaven and the first earth passed away, and there is no longer any sea. (Rev 21:1, LSB)

And the city has no need of the sun or of the moon to shine on it, for the glory of God has illumined it, and its lamp is the Lamb. And the nations will walk by its light, and the kings of the earth will bring their glory into it. (Rev 21:23-24, LSB)

4. What do you observe about Believers?

Then he showed me a river of the water of life, bright as crystal, coming from the throne of God and of the Lamb, in the middle of its street. On either side of the river was the tree of life, bearing twelve kinds of fruit, yielding its fruit every month; and the leaves of the tree were for the healing of the nations. And there will no longer be any curse; and the throne of God and of the Lamb will be in it, and His slaves will serve Him; and they will see His face, and His name will be on their foreheads. And there will no longer be any night, and they will not have need of the light of a lamp nor the light of the sun, because the Lord God will illumine them, and they will reign forever and ever. (Rev 22:1-5, LSB)