From a treatise Against Heresies by Saint Irenaeus, bishop
When Christ comes, God will be seen by men
There is one God, who by his word and wisdom created all things and set them in order. His Word is our Lord Jesus Christ, who in this last age became man among men to unite end and beginning, that is, man and God.
The prophets, receiving the gift of prophecy from this same Word, foretold his coming in the flesh, which brought about the union and communion between God and man ordained by the Father. From the beginning the word of God prophesied that God would be seen by men and would live among them on earth; he would speak with his own creation and be present to it, bringing it salvation and being visible to it. He would free us from the hands of all who hate us, that is, from the universal spirit of sin, and enable us to serve him in holiness and justice all our days. Man was to receive the Spirit of God and so attain to the glory of the Father.
The prophets, then, foretold that God would be seen by men. As the Lord himself says: Blessed are the clean of heart, for they shall see God. In his greatness and inexpressible glory no one can see God and live, for the Father is beyond our comprehension. But in his love and generosity and omnipotence he allows even this to those who love him, that is, even to see God, as the prophets foretold. For what is impossible to men is possible to God.
By his own powers man cannot see God, yet God will be seen by men because he wills it. He will be seen by those he chooses, at the time he chooses, and in the way he chooses, for God can do all things. He was seen of old through the Spirit in prophecy; he is seen through the Son by our adoption as his children, and he will be seen in the kingdom of heaven in his own being as the Father. The Spirit prepares man to receive the Son of God, the Son leads him to the Father, and the Father, freeing him from change and decay, bestows the eternal life that comes to everyone from seeing God.
As those who see light are in the light sharing its brilliance, so those who see God are in God sharing his glory, and that glory gives them life. To see God is to share in life.
