Book 1 - Knowledge of God the Creator
Chapter 13 - One essence of God, which contains Three Persons
Sections 21-29 - Refutation of anti-Trinitarian heresies
Section 25 - The divine nature is common to all three Persons
If only the Father had deity inherently, the Son and Spirit would not really be God.
Section 26 - The subordination of the incarnate Word to the Father is no counterevidence
The Son is equal in power and glory with the Father (John 17:3).
The Son did not lose that glory while on earth (Phil 2:7), but it was hidden.
In that hiddenness, the Father was greater than the Son (John 14:28).
Jesus is everlasting (Heb 1:10), thus is as much God as the Father is.
John 1:1; 1 John 5:20.
Section 27 - Our adversaries falsely apeal to Irenaeus
They take him out of context when he says the Father is the God of Israel. He was not asserting that Jesus is not as much God; he was keeping the God of OT and of NT the same God.
Section 28 - The appeal to Tertullian also is of no avail
His wording is tricky, but he opposes the idea that Christ can't be God without being the same as the Father.
Section 29 - All acknowledged doctors of the church confirm the doctrine of the Trinity
When Justin, Ignatius or Augustine teach that unity or eternity is in the Father, they do not mean to deny that the Son is inherently God.
Undue speculation is a root cause of Trinitarian error.