13 Thus the name which expresses His nature proves the truth of our confession of the faith. For the name, which indicates any single substance, points out also any other substance of the same kind; and, in this instance, there are not two substances but one substance, of the one kind. For the Son of God is God; this is the truth expressed in His name. The one name does not embrace two Gods; for the one name God is the name of one indivisible nature. For since the Father is God and the Son is God, and that name which is peculiar to the Divine nature is inherent in Each, therefore the Two are One.
For the Son, though He subsists through a birth from the Divine nature, yet preserves the unity in His name; and this birth of the Son does not compel loyal believers to acknowledge two Gods, since our confession declares that Father and Son are One, both in nature and in name. Thus the Son of God has the Divine name as the result of His birth. Now the second step in our demonstration was to be that of showing that it is by virtue of His birth that He is God. I have still to bring forward the evidence of the Apostles that the Divine name is used of Him in an exact sense; but for the present I purpose to continue our enquiry into the language of the Gospels.
Source: On the Trinity (New Advent)