28 May the faith of the Gospel ever profit thus by the rash contentions of the ungodly to defend itself with the weapons of their attack, and conquering with the arms prepared for its destruction, prove that the words of the one Spirit are the doctrine of the one faith! For Christ is none other than He is preached, namely the true God, and abiding in the glory of the one true God. Just as He proclaims Himself Lord out of the law, even when He seems to deny the fact, so in the Gospels He proves Himself the true God, even when He appears to confess the opposite.
To escape the acknowledgment that He is the true God, the heretics plead that He said, And this is life eternal, that they should know You, the only true God. and Him Whom You sent, even Jesus Christ. When He says, You, the only true God, they think He excludes Himself from the reality of God by the restriction of solitariness; for the only true God cannot be understood except as a solitary God. It is true the Apostolic faith does not suffer us to believe in two true Gods, for nothing which is foreign to the nature of the one God can be put on equality with the truth of that nature; and there is more than one God in the reality of the one God, if there exists outside the nature of the only true God a true God of another kind, not possessing by virtue of His birth the same nature with Him.
Source: On the Trinity (New Advent)