Since he has taught that three things tend toward maturity in Christ—faith, understanding and love—he here brings them all into a brief compass. He is now praying that God will bestow all these gifts upon the Ephesians. Note the sequence he has followed: He spoke first of faith, “that you may have Christ dwelling in the inner man in your hearts through faith.” Now he speaks of understanding by saying “so that you may comprehend with all the saints the breadth, length and depth.” Again he adds with regard to love, “to know the love that surpasses knowledge.”
God is through all and in all, and is all things and the source of all, through whom all things come and over all. In this aspect the task of understanding is to note and know what “the breadth, the length, the height and the depth” of divine grace. How all these exist together or may be understood to exist in God and according to these aspects requires another, higher comprehension.… Hence he prays finally that the Ephesians may understand them all together. And so that they will not despair through their inability to comprehend them together, he adds: “so that you may be able to comprehend with all the saints.” Therefore the saints comprehend these things together and can expound them.
What is meant when Paul speaks of “length and breadth and depth and height?” Think of a sphere. The length is the same as the breadth and the height the same as the depth. So too all is proportional within the immeasurable infinity of God. A sphere is enclosed in a definite manner. God, being unenclosed, not only fills all things but exceeds all things. God is not confined but has everything within himself, so that he is the only one to be reckoned infinite. We cannot sufficiently thank him for the fact that, being so great, he deigned through Christ to visit human beings when they were subject to death and sin.
The height is the measure of the majesty of the Lord.… The length is the passion of the Lord’s cross, by which believers are sealed. The breadth is seen in Pentecost, when the Holy Spirit is coming down upon all believers.
The divine mind of the apostle did not imagine this fourfold figure of the cross to no purpose. He knew that this figure, which is divided into four segments from the common center, represents the power and providence of the one displayed upon it. This dimensionality runs through all things. For this reason he calls each of four projections by its own name. By the height he means what is above, by the depth the underworld, by the length and breadth the intermediate domain which is under the control of his all-governing power. Hence the worship of the cross is viewed in relation to the fourfold figure of the cross. The heavenly order is symbolically paying its devotion to the Lord in the upper part, the cosmic order in the middle part and even the infernal order in the lower part.
Thus is his prayer now again, the very same as when he began. For what were his words in the beginning? "That the God of our Lord Jesus Christ, the Father of glory may give unto you a Spirit of wisdom and revelation in the knowledge of Him; having the eyes of your heart enlightened, that you may know what is the hope of His calling, what the riches of the glory of His inheritance in the saints; and what the exceeding greatness of His power to us-ward who believe." And now again he says the same. "That ye may be strong to apprehend with all the saints what is the breadth, and length, and height, and depth;" i.e., to know perfectly the mystery which has been providentially ordered in our behalf: "and the breadth, and length, and height, and depth;" that is, too, the immensity of the love of God, and how it extends every where. And he outlines it by the visible dimensions of solid bodies, pointing as it were to a man. He comprehends the upper and under and sides. I have thus spoken indeed, he would say, yet is it not for any words of mine to teach you these things; that must be the work of the Holy Spirit. "By His might," says he, is it that you must be "strengthened" against the trials that await you, and in order to remain unshaken; so that there is no other way to be strengthened but by the Holy Ghost, both on account of trials and carnal reasonings.
But how does Christ dwell in the hearts? Hear what Christ Himself says, "I and my Father will come unto him, and make our abode with him." [John 14:23] He dwells in those hearts that are faithful, in those that are "rooted" in His love, those that remain firm and unshaken.
"That ye may be" thoroughly "strong," says he; so that there is great strength needed.
"That ye may be filled unto all the fullness of God."
What he means is this. Although the love of Christ lies above the reach of all human knowledge, yet shall you know it, if you shall have Christ dwelling in you, yea, not only shall know from Him this, but shall even "be filled unto all the fullness of God;" meaning by the "fullness of God," either the knowledge how God is worshipped in the Father, the Son, and the Holy Ghost, or else urging them thus to use every effort, in order to be filled with all virtue, of which God is full.
Let us think first about physical “breadth and length, depth and height” in order that we may be able to pass through these physical dimensions to their spiritual dimensions. For the sake of argument, let the physical length be that of heaven and earth, that is, of the whole world, from east to west. Let the breadth be from south to north. Let the depth be from the abyss and the infernal regions. Let the height be to all that is elevated above the heavens. But they say that the earth is round and rotates as a sphere. Roundness has no breadth and length, height and depth, but is proportional in all dimensions. Hence we are necessarily forced to understand spiritually by height the angels and forces above and by depth those powers below and what is beneath them. By length and breadth we speak spiritually of that which occupies the middle place between those above and those below. The consequence is that one draws near as a neighbor either to those things above or to those below. Whatever begins to advance one’s path toward better things so as to rise to the heavenly height, that is what Paul is calling length. Whatever brings one to the lower things as one lapses toward vice he is calling breadth.
[AD 370] Gaius Marius Victorinus on Ephesians 3:18