Irenaeus on Theosis

It leads us to the endless and perfect end, teaching us beforehand the future life that we shall lead, according to God, and with gods; after we are freed from all punishment and penalty which we undergo, in consequence of our sins, for salutary discipline.

God became man that man might become God.

Our Father in Heaven was begotten on a previous heavenly world by His Father; He was begotten by a still more ancient Father; and so on from generation to generation, from one heavenly world to another.

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

[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.

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.” . . .

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.