Nicene and Post-Nicene Fathers, Vol. II:
City of God: Chapter 22

Chapter 22.—Whether the God Whom the Christians Serve is the True God to Whom Alone Sacrifice Ought to Be Paid.

But it may be replied, Who is this God, or what proof is there that He alone is worthy to receive sacrifice from the Romans?  One must be very blind to be still asking who this God is.  He is the God whose prophets predicted the things we see accomplished.  He is the God from whom Abraham received the assurance, “In thy seed shall all nations be blessed.” 1298   That this was fulfilled in Christ, who according to the flesh sprang from that seed, is recognized, whether they will or no, even by those who have continued to be the enemies of this name.  He is the God whose divine Spirit spake by the men whose predictions I cited in the preceding books, and which are fulfilled in the Church which has extended over all the world.  This is the God whom Varro, the most learned of the Romans, supposed to be Jupiter, though he knows not what he says; yet I think it right to note the circumstance that a man of such learning was unable to suppose that this God had no existence or was contemptible, but believed Him to be the same as the supreme God.  In fine, He is the God whom Porphyry, the most learned of the philosophers, though the bitterest enemy of the Christians, confesses to be a great God, even according to the oracles of those whom he esteems gods.

Footnotes

Gen. 22.18.