What benefits do we receive from knowing that the Father of our Lord Jesus Christ, His Son, and the Holy Spirit alone are the true God and that there is no other?
Answer: First, this benefit: since it is our highest good to know God aright, and since our bodies and souls were created and redeemed at a price so that they might be temples of God and He might be glorified in us, it is only through the knowledge of the one true God — Father, Son, and Holy Spirit — that we know that this takes place in us.
Second, it has the benefit that when we pray, we know and think about which God we are calling upon — the true God, who is truthful in His promises, who alone can help inasmuch as He alone is an almighty God, and who alone will help inasmuch as He is a truthful and faithful Father.
The heathen, on the other hand, worship gods who are not really gods but inventions of the Father of Lies, the Devil. They neither can help, because they are not God, nor will help, because they are inventions of the Devil, who is a liar and a murderer.
Third, it follows from this that unless we wish to apostatize from the highest good and forfeit the true invocation of God, we cannot also serve strange gods, either inwardly or outwardly.