21 This Life is the Light of men, the Light which lightens the darkness. To comfort us for that powerlessness to describe His generation of which the prophet speaks, the Fisherman adds, And the darkness comprehended Him not. The language of unaided reason was baffled and silenced; the Fisherman who lay on the bosom of the Lord was taught to express the mystery. His language is not the world's language, for He deals with things that are not of the world. Let us know what it is, if there be any teaching that you can extract from his words, more than their plain sense conveys; if you can translate into other terms the truth we have elicited, publish them abroad. If there be none— indeed, because there are none— let us accept with reverence this teaching of the fisherman, and recognise in his words the oracles of God. Let us cling in adoration to the true confession of Father and Son, Unbegotten and Only-begotten ineffably, Whose majesty defies all expression and all perception. Let us, like John, lie on the bosom of the Lord Jesus, that we too may understand and proclaim the mystery.
Source: On the Trinity (New Advent)