And with respect to His having descended among men, He was “previously in the form of God;” and through benevolence, divested Himself (of His glory), that He might be capable of being received by men. But He did not, I imagine, undergo any change from “good to evil,” for “He did no sin;” nor from “virtue to vice,” for “He knew no sin.” Nor did He pass from “happiness to misery,” but He humbled Himself, and nevertheless was blessed, even when His humiliation was undergone in order to benefit our race.
Nor was there any change in Him from “best to worst,” for how can goodness and benevolence be of “the worst?” Is it befitting to say of the physician, who looks on dreadful sights and handles unsightly objects in order to cure the sufferers, that he passes from “good to evil,” or from “virtue to vice,” or from “happiness to misery?” And yet the physician, in looking on dreadful sights and handling unsightly objects, does not wholly escape the possibility of being involved in the same fate.
But He who heals the wounds of our souls, through the word of God that is in Him, is Himself incapable of admitting any wickedness. But if the immortal God— the Word — by assuming a mortal body and a human soul, appears to Celsus to undergo a change and transformation, let him learn that the Word, still remaining essentially the Word, suffers none of those things which are suffered by the body or the soul; but, condescending occasionally to (the weakness of) him who is unable to look upon the splendours and brilliancy of Deity, He becomes as it were flesh, speaking with a literal voice, until he who has received Him in such a form is able, through being elevated in some slight degree by the teaching of the Word, to gaze upon what is, so to speak, His real and pre-eminent appearance.
Source: Against Celsus (New Advent)