“For St. Irenaeus not only made his own the special expressions of Johannine mysticism, but assimilated them in a very personal way, as this other beautiful text indicates:
In His wonderful greatness and glory, ‘no man can see God and live’, for the Father is incomprehensible; but in His love and His humanity, and because He can do all things, He has granted even this to those who love Him: to see God, as the prophets foretold it. For ‘what is impossible to men is possible to God’. Of himself, indeed, man cannot see God. But He, when He wills it, is seen by men, by those He wills, when He wills it and how He wills it. For God has power to do anything: seen in a prophetic way through the Spirit, He is seen, through the Son, adoptively, and He will be seen paternally in the Kingdom of heaven – the Spirit preparing for the Son of God, the Son leading him to the Father, and the Father giving him incorruptibility for eternal life, which comes to each one from the fact that he sees God.
In the same spirit of Johannine mysticism, Irenaeus has us go on from the vision of God to the divine life that is communicated:
Just as those who see the light are in the light and share in its splendor, so those who see God are in God, participating in His splendor. But the splendor gives them life: thus they participate in life, those who see God. And it is because of this that He who is incomprehensible and intangible and invisible gives Himself to be seen, to be understood, to be grasped, so as to life to those who grasp and see Him by faith. For, just as His greatness is unfathomable, so His goodness is ineffable, the goodness by which, being seen, He gives life to those who see Him. Since to live without life is impossible, the possibility (huparxis) of life comes from participation in God, and participation in God is to know Him and to enjoy His goodness. Thus men see God in such a way that they live, made immortal by the sight and truly attaining God.”
(The Spirituality of the New Testament & The Fathers, pp 229-230)