48 But there is no danger that the one faith will cease to be such through diversity in its preaching. The Evangelist had taught that our Lord said, He that has seen Me, has seen the Father also. But has Paul, the teacher of the Gentiles, forgotten or kept back the meaning of the Lord's words, when he says, Who is the image of the invisible God ? I ask whether He is the visible likeness of the invisible God, and whether the infinite God can also be presented to view under the likeness of a finite form?
For a likeness must needs repeat the form of that of which it is the likeness. Let those, however, who will have a nature of a different sort in the Son determine what sort of likeness of the invisible God they wish the Son to be. Is it a bodily likeness exposed to the gaze, and moving from place to place with human gait and motion? Nay, but let them remember that according to the Gospels and the Prophets both Christ is a Spirit and God is a Spirit. If they confine this Christ the Spirit within the bounds of shape and body, such a corporeal Christ will not be the likeness of the invisible God, nor will a finite limitation represent that which is infinite.
Source: On the Trinity (New Advent)