In the Athanasian Creed, the writers were doing their best to describe the Jesus found in the New Testament with as much clarity as possible. They did this by means of introducing a description that we may have never used when thinking or talking about Jesus.
He is God from the essence of the Father, begotten before time;
What makes someone or something who they are? Their essence. By way of a somewhat silly example, it may help to consider a peanut butter and jelly sandwich.
What is the essence of a peanut butter and jelly sandwich? It can’t be the bread, because other types of sandwiches are made with bread. The essence of that particular sandwich is the peanut butter and jelly. The way you can tell the difference between a ham and cheese and a PB&J is not by the bread, but by what’s in between the bread.
The same type of thing can be said about Jesus.
He is who he is because of the Father. That which makes the Father God, is what makes Jesus God. Note, the specificity with the creed. Jesus is God from the essence of the Father. It does not say that Jesus is the Father from the essence of the Father. There is no confusion with the creed as to who Jesus is and to who the Father is. Jesus and the Father are two of the three unique persons of the divine Godhead—the Trinity.
Furthermore, Jesus comes from the Father. More precisely, the creed says that Jesus is begotten before time from the Father. In other words, Jesus is and has been—for all of eternity past—coming from the Father. You could say he has been proceeding from the Father for all time.
It must be stated, before going further, that this idea of the Son eternally coming from the Father is not one that is held by all believers. It is a belief I hold to and one I, of course believe is biblical, but there would be others who would disagree. That being said, let’s move forward.
This is where your head could start to hurt, but the Scriptures present a Jesus who has been the Son of God forever. God—the Father, Son, and Holy Spirit—has existed forever and for as long as God has existed, the Son has been coming from— or in using the language of the creed, begotten of—the Father.
This is, of course, exactly what is said in the letter of 1 John: “And we have seen and testify that the Father has sent the Son to be the Savior of the world” (1 Jn. 4:14, LEB).