Hilary of Poitiers

(vii. de Trin) He does not mean the sight of the bodily eye: for His fleshly part, born of the Virgin, doth not avail towards contemplating the form and image of God in Him; but the Son of God being known with the understanding, it follows that the Father is known also, forasmuch as He is the image of God, not differing from but expressing His Author1. For our Lord’s expressions do not speak of one person solitary and without relationship, but teach us His birth. The Father also excludes the supposition of a single solitary person, and leaves us no other doctrine but that the Father is seen in the Son, by the incommunicable likeness of birth.