In the former discourse, so far as the subject impressed us, and so far as our poverty of understanding attained to, we have spoken by occasion of the words of the Gospel, where it is written: “The Son cannot do anything of Himself, but what He sees the Father doing,”— what it is for the Son— that is, the Word, for the Son is the Word— “to see;” and as all things were made by the Word, how it is to be understood that the Son first sees the Father doing, and then only Himself also does the things which He has seen done, seeing that the Father has done nothing except by the Son.
For all things were made by Him, and without Him was nothing made. We have not, however, delivered to you anything as fully explained, and that because we have not understood anything thus clearly set forth. For, indeed, speech sometimes fails even where the understanding makes way; how much more does speech suffer defect, where the understanding has nothing perfect! Now, therefore, as the Lord gives us, let us briefly run over the passage, and even today complete the due task.
Should there perchance remain somewhat of time or of strength, we will reconsider (so far as it may be practicable for us and with you) what it is for the Word “to see” and “to be shown to;” since, in fact, all that is here spoken is such that, if understood according to man's sense, carnally, the soul full of vain fancies makes for us only certain images of the Father and the Son, just as of two men, the one showing, the other seeing; the one speaking, the other hearing—all which are idols of the heart. And if now at length idols have been cast down from their own temples, how much more ought they to be cast down from Christian hearts!
Source: Tractates on the Gospel of John (New Advent)