37 The fact is obvious from His own words. For He says to Hosea the prophet, I will no more have mercy upon the house of Israel, but will altogether be their enemy. But I will have mercy upon the children of Judah, and will save them in the Lord their God. Here God the Father gives the name of God, without any ambiguity, to the Son, in Whom also He chose us before countless ages. Their God, He says, for while the Father, being Unoriginate, is independent of all, He has given us for an inheritance to His Son. In like manner we read, Ask of Me, and I will give You the Gentiles for Your inheritance. None can be God to Him from Whom are all things, for He is eternal and has no beginning; but the Son has God, from Whom He was born, for His Father. Yet to us the Father is God and the Son is God; the Father reveals to us that the Son is our God, and the Son teaches that the Father is God over us. The point for us to remember is that in this passage the Father gives to the Son the name of God, the title of His own unoriginate majesty. But I have commented sufficiently on these words of Hosea.
Source: On the Trinity (New Advent)