The pagan (Neoplatonist) philosopher Porphyry argues that, based on an Oracle from Apollo, the Jews worship the true God, while the Christians violate that by worshiping Jesus as God instead--though Porphyry admits that Jesus was at least a good and virtuous man (even if he "deserved" what he got at the hand of the Jews).
According to Augustine, the sinister goal here (whether Porphyry actually knows it or is simply buying into demonic claims) is to gain our attention by praising Christ, and then lead us aside from "that road to eternal salvation upon which one who becomes a Christian enters."
Whether one is arguing that "Christ was a criminal, executed by right-thinking judges;," or that "he was a sincerely pious man--but merely a man", the result is the same.
Either way, these arguments contradict each other (despite both at least nominally coming from pagan gods) and are internally inconsistent. For example, how could Jesus have been a "good man" if he led so many people astray when he lied about being God?
But we don't even need to go this far, we can simply compare the wicked worship and practice of the pagans with the virtuous worship and actions of the Christians to see that the latter is the true and right path. The we learn from the consistent and holy Word of God, the Scripture, wherein those who sacrifice to false gods will be put to death. Christians, on the other hand, "who form His City, are His best and most worthy sacrifice."
In sum, the only true "commonwealth" is the one wherein God is worshiped and obeyed, where the citizens "live by that faith of the just which works through that charity which loves God as He should be loved and one's neighbor as oneself." Where this does not exist there can be no true commonwealth and no true working for the common good.