Ephesians 3:19

19.And to know the love of Christ. By those dimensions Paul means nothing else than the love of Christ, of which he speaks afterwards. The meaning is, that he who knows it fully and perfectly is in every respect a wise man. As if he had said, “In whatever direction men may look, they will find nothing in the doctrine of salvation that does not bear some relation to this subject.” The love of Christ contains within itself the whole of wisdom, so that the words may run thus: that ye may be able to comprehend the love of Christ, which is the length and breadth, and depth, and height, that is, the complete perfection of all wisdom. The metaphor is borrowed from mathematicians, taking the parts as expressive of the whole. Almost all men are infected with the disease of desiring to obtain useless knowledge. It is of great importance that we should be told what is necessary for us to know, and what the Lord desires us to contemplate, above and below, on the right hand and on the left, before and behind. The love of Christ is held out to us as the subject which ought to occupy our daily and nightly meditations, and in which we ought to be wholly plunged. He who is in possession of this alone has enough. Beyond it there is nothing solid, nothing useful, — nothing, in short, that is proper or sound. Though you survey the heaven and earth and sea, you will never go beyond this without overstepping the lawful boundary of wisdom.

Which surpasseth knowledge. A similar expression occurs in another Epistle:

“the peace of God, which surpasseth all understanding, shall keep your hearts and minds through Christ Jesus.”
(Philippians 4:7)

No man can approach to God without being raised above himself and above the world. On this ground the sophists refuse to admit that we can know with certainty that we enjoy the grace of God; for they measure faith by the perception of the bodily senses. But Paul justly contends that this wisdom exceeds all knowledge; for, if the faculties of man could reach it, the prayer of Paul that God would bestow it must have been unnecessary. Let us remember, therefore, that the certainty of faith is knowledge, but is acquired by the teaching of the Holy Spirit, not by the acuteness of our own intellect. If the reader desire a more full discussion of this subject, he may consult the “Institutes of the Christian Religion.”

That ye may be filled. Paul now expresses in one word what he meant by the various dimensions. He who has Christ has everything necessary for being made perfect in God; for this is the meaning of the phrase,the fullness of God. Men do certainly imagine that they have entire completeness in themselves, but it is only when their pride is swelled with empty trifles. It is a foolish and wicked dream, that by the fullness of God is meant the full Godhead, as if men were raised to an equality with God.