As to the passage in question, the Apostle Paul prays for the believers in Ephesus that they may really know about the love of God. Given that this is found in the larger context of what starts a few verses earlier, let me offer that fuller text (verses 14-19) here:

For this reason I bow my knees before the Father, from whom every family in heaven and on earth is named, that according to the riches of his glory he may grant you to be strengthened with power through his Spirit in your inner being, so that Christ may dwell in your hearts through faith--that you, being rooted and grounded in love, may have strength to comprehend with all the saints what is the breadth and length and height and depth, and to know the love of Christ that surpasses knowledge, that you may be filled with all the fullness of God.

What an incredible passage that is. And as mentioned, one exceedingly important Christian preacher who never fails to do full justice to the biblical text is Martyn Lloyd-Jones. He spends eight whole sermons on just these two verses, which in turn comprise eight whole chapters in his third of eight volumes on Ephesians. That third volume is The Unsearchable Riches of Christ, first published in 1979.

The Unsearchable Riches of Christ: An Exposition of Ephesians 3 by Lloyd-Jones, D. Martyn (Author)

Let me quote some of what is found in Chapters 16-23. One paragraph makes for a useful introduction to this theme:

We are about to look into something which is so glorious and endless that it will be the theme of contemplation of all the saints, not only in this world, but also in the world which is to come. We shall spend our eternity in gazing upon it, and wondering at it, and in being astounded by it. But it is our business to start upon this here and now in this life. It has ever been one of the characteristics of the greatest saints that they have spent much time in meditating upon the love of Christ to themselves and to all God's people. Nothing has given them greater joy. Indeed this is a characteristic of love at all levels; it delights in thinking not only of the object of its love, but also of the love it receives. Nothing therefore should give greater joy to all God's people than to meditate upon this love of Christ. Indeed, our chief defect as Christians is that we fail to realize Christ's love to us. How often have you thought about this? We spend time thinking about our activities and our problems, but the most important necessity in the Christian life is to know Christ's love to us, and to meditate upon it. This has always been the spring and the source of the greatest activity that has ever been manifested in the long history of the Christian Church. (p. 219)

In his prior chapter he begins it with these words:

These two verses tell us what the Apostle's real object was in praying for these Ephesian Christians. All the previous petitions prepare for and lead up to this petition. They were essential as preparation, but they are not ends in themselves; they are designed to lead on to this grand objective. We find ourselves, as it were, upon the pinnacle of Christian truth. There is nothing higher than this. God grant us His Spirit that we may consider it aright! We are in a rarefied atmosphere; in a place to which, alas, we are not accustomed. Far too many of us are content to spend our time in the lowlands and the plains amid the mists and the other characteristics of that level of life. (p. 205)

He goes on to say this:

How, then, is this experience to be gained? It seems clear that it is a matter of degree. There is a preliminary awareness of the love of God; but compared with that which the Apostle has in mind here, it is, in the words of a hymn, but 'weak and faint'. Indeed, the love we are now contemplating is so much greater than this awareness, that all who have ever had an experience of it are tempted to say that they had never known the love of God before. They feel that they had known of it, and known about it, but had not really known the love itself. That is the difference between the two degrees of knowledge of God's love. We must never fall into the error of imagining that because we are Christians we therefore know all about the love of God. Most of us are but as children paddling at the edge of an ocean; there are abysmal depths in this love of God of which we know nothing. The Apostle is praying that these Ephesians, and we with them, may go out into the depths and the deeps, and discover things which we have never even imagined. (p. 207)

Lloyd-Jones mentions Philippians 3:10 where Paul speaks of wanting to know Christ even more, and then says this:

Love cannot be satisfied. Once you know this Person and begin to love Him, you feel that all you have received is not enough, you want more and more. This is what Paul is praying for these Ephesians. He longs for them also to know Christ, because to know Him is to know His love. The more we know Him the more we shall know His love toward us. These things are indivisible, and cannot be separated. (p. 209)

I finish with five final paragraphs:

We find constantly in Christian biographies, as I have had occasion to remark several times, that every man who has ever any sort of impression of the love of God has always had a feeling that it is overwhelming, and has doubted whether he would be able to endure it. When Isaiah saw and felt something of it, that was his reaction. John on the Isle of Patmos tells us that he 'fell down as one dead'. The love of God is so great and powerful that a man feels his physical frame beginning to crack beneath it. Many Christian people, when they have suddenly had an awareness of this love of God, have literally fainted and become unconscious.

An instance of this is found in the accounts of the Revival which took place in Wales in 1904-6 and which is associated with a man called Evan Roberts. Evan Roberts had an experience of this nature which not only proved to be the turning point in his life but also a crucial moment in the story of that Revival. He stood up in a meeting in a chapel, and suddenly this love of God so came upon him that he literally fell to the ground. Many present thought that he was actually dead. What had happened was that he had had a realization of this overwhelming love of God. That is why we need to be 'strengthened'.

Have we ever been caused to feel faint by the love of God? Do we know what it is -- to use the language of Solomon's Song of Songs to be 'sick of love' (2:5), to experience its marvellous power to such an extent that our strength seems to leave us, and we are overwhelmed by it?

A further reason why we need to be made able to comprehend it, is that it is love alone that can recognize love. We need to be 'rooted and grounded in love' in order to comprehend this love of God. Love alone recognizes love, love alone understands love; indeed, it is love alone that can receive love. This is a realm where intellect almost appears ridiculous. It is useless to put intellect to meet love; it is incompetent in this realm. Like attracts like. You must have love in your heart if you are going to know love and experience it. There are people who read the Bible and yet hate God, for there is no love in their hearts. It is love alone that can appreciate love. This principle obtains in many realms. You will not be able to appreciate the most glorious music if you are not musical. There are people who are almost driven mad by the sound of some great symphony because they are devoid of a musical faculty. Likewise people can walk through the finest Art galleries and be bored. They are lacking in an artistic sense.

The same is true in respect of love. There are people who remain utterly unmoved by the most eloquent and moving sermons on the love of God, or by singing of great hymns on the same theme. It is because they have not been 'rooted and grounded in love'. They have not been made fully able to receive it and to comprehend it. That is why we have had to deal so thoroughly with the preparation. We should thank God for the fact that it is love that enables us to comprehend the love of Christ, for it is this that ensures the possibility of all saints knowing it. (pp. 213-214)

I have often said that when I pen a devotional piece dealing with biblical spirituality and the like, I am writing for myself as much as for anyone else. And when it comes to something like this grand reality of the love of God, that is absolutely the case. Even if some of my readers may not need an article like this all that much, I most certainly do.

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