In the next place, when the philosophers of the Porch, who assert that the virtue of God and man is the same, maintain that the God who is over all things is not happier than their wise man, but that the happiness of both is equal, Celsus neither ridicules nor scoffs at their opinion. If, however, holy Scripture says that the perfect man is joined to and made one with the Very Word by means of virtue, so that we infer that the soul of Jesus is not separated from the first-born of all creation, he laughs at Jesus being called “Son of God,” not observing what is said of Him with a secret and mystical signification in the holy Scriptures.
But that we may win over to the reception of our views those who are willing to accept the inferences which flow from our doctrines, and to be benefited thereby, we say that the holy Scriptures declare the body of Christ, animated by the Son of God, to be the whole Church of God, and the members of this body— considered as a whole— to consist of those who are believers; since, as a soul vivifies and moves the body, which of itself has not the natural power of motion like a living being, so the Word, arousing and moving the whole body, the Church, to befitting action, awakens, moreover, each individual member belonging to the Church, so that they do nothing apart from the Word.
Since all this, then, follows by a train of reasoning not to be depreciated, where is the difficulty in maintaining that, as the soul of Jesus is joined in a perfect and inconceivable manner with the very Word, so the person of Jesus, generally speaking, is not separated from the only-begotten and first-born of all creation, and is not a different being from Him? But enough here on this subject.
Source: Against Celsus (New Advent)