Deuteronomy 8:19

Thee. Hebrew, "I attest this day against you, (Septuagint add heaven and earth,) that you shall," &c. God had already forbidden the worship of strange gods, Exodus xx. 3. He now threatens to punish the transgressors most severely. All nations have deemed it criminal to abandon the religion of their ancestors, unless when there is evident proofs of its absurdity, as was the case when so many embraced the doctrine of Jesus Christ, for which they were so cruelly persecuted. The Athenians would not suffer a word to be spoken against their gods; (Josephus, contra Apion ii.) and Cicero (Leg. ii.) lays down this as a law, "Let no one have gods to himself, nor any new ones: let him not adore, even in private, strange gods; unless they have been publicly acknowledged." (Calmet)