Over against all of the current inanities that are being said about Jesus Christ, why do Christians declare Jesus to be God and the only mediator between God and humanity? The second-century theologian Irenaeus (died c.202), who also had to face similar inanities in the form of Valentinian Gnosticism and Marcionism, can help us answer this question. For Irenaeus, the only way we can know and see God was through love; and not our love for him, but rather, through his love for us. We know God because he first loved us. Thus Irenaeus writes of Christ: “So he united man with God and brought about a communion of God and man, we being unable in any other wise to have part in incorruptibility, had it not been for his coming to us.” (Demonstration 31).
Humanity cannot see God the Father by its own powers (Against Heresies 1.20.5). Not only is the Father beyond perception and thus unknowable and invisible, but mankind is lost in sin because of Adam’s fall (Against Heresies 3.23.2; 5.1.3, 16.3, 21.1, 34.2; Demonstration 31, 37), and thus incapable by nature of seeing God and saving itself (sine Spiritu Dei salvari non possumus) (Against Heresies 3.18.2, 20.2-3; 4.13.3; 5.9.2, 12.3).
It is essential to bear in mind that for Irenaeus no created reality can be commensurate with God, even in heaven. God is always the Giver and humanity the recipient. See Against Heresies 4.11.2: “Et hoc Deus ab homine differt, quondam Deus quidem facit, homo autem fit.”
Although human beings cannot know God in their own strength, it does not follow that God cannot make himself known to them. Human beings can know God through divine love and are saved by this love.
Now, it is only through the Son that the Father is revealed. The Son is the agnitio Patris, mensura Patris, the manifestatio Patris, the visible Patris. The Son is the necessary mediator in imparting to men and women the knowledge of God the Father.
This revealing activity by the Son of the Father is a continuous one. It began at creation and will stretch into eternity. For Irenaeus, the Word was always present with God. Though Irenaeus does not define the relationship between Father and Son within the Godhead, his writings definitely imply the eternal generation of the Word. God was never without his Logos. The Son has, therefore, always been manifesting the Father.
This revelation of the Father by the Son depends on the good will of the Father (beneplacitum Patris) [J. Ochagavia, Visible Patris Filius (Rome, 1964), 66], for it is the Father that sends the Son (Against Heresies 4.11.2). The Son manifests the Father according to the Father’s benevolent disposition (Against Heresies 4.20.5). The Father’s transcendence rules out the possibility of his appearing to men and women; but the Father’s goodness leads to the sending of his Son to fallen humanity (Against Heresies 4.34.5).