Irenaeus on Theosis

How, then, shall he become a God, who has not as yet been made a man? Or how can he be perfect who was but lately created? How, again, can he be immortal, who in his mortal nature did not obey his maker? For it must be that thou, at the outset, shouldest hold the rank of a man, and then afterwards partake of the glory of God.

Do we cast blame on him [God] because we were not made gods from the beginning, but were at first created merely as men, and then later as gods? Although God has adopted this course out of his pure benevolence, that no one may charge him with discrimination or stinginess, he declares, “I have said, ye are gods; and all of you are sons of the Most High.” . . .

[T]he Word became flesh and the Son of God became the Son of Man: so that man, by entering into communion with the Word and thus receiving divine sonship, might become a son of God.

Our Lord Jesus Christ . . . became what we are, so that He might bring us to be even what He Himself is.