All of these things we've been saying about the Christian faith likewise apply to the Old Testament believers, who also were justified by faith in the (then-still-to-come) Gospel of Jesus Christ. Their sins, too, were dealt with on the cross, and all of us are united in one heavenly city focused on the worship of God.
This is the most glorious city of God; this is the city which knows and worships one God: she is celebrated by the holy angels, who invite us to their society, and desire us to become fellow-citizens with them in this city; for they do not wish us to worship them as our gods, but to join them in worshipping their God and ours; nor to sacrifice to them, but, together with them, to become a sacrifice to God. Accordingly, whoever will lay aside malignant obstinacy, and consider these things, shall be assured that all these blessed and immortal spirits, who do not envy us (for if they envied they were not blessed), but rather love us, and desire us to be as blessed as themselves, look on us with greater pleasure, and give us greater assistance, when we join them in worshipping one God, Father, Son, and Holy Ghost, than if we were to offer to themselves sacrifice and worship.Chapter 26:
Even the pagans that have some dim understanding of this truth cannot quite bring themselves to confess it. Porphyry understands and sees it, but rejects it at the end because of his own sin.