For as those who see the light are within the light, and partake of its brilliancy; even so, those who see God are in God, and receive of His splendour. But [His] splendour vivifies them; those, therefore, who see God, do receive life.
… For the glory of God is a living man; and the life of man consists in beholding God. For if the manifestation of God which is made by means of the creation, affords life to all living in the earth, much more does that revelation of the Father which comes through the Word, give life to those who see God.
Irenaeus of Lyons
Against Heresies, Book IV
Chapter XX