May be able to comprehend with all saints {i} what is the breadth, and length, and depth, and height;

(i) How perfect that work of Christ is in every part.

People's New Testament

3:18 May be able to comprehend. Unless they were rooted and grounded in love (Eph 3:17) and the love of God shed abroad in their hearts (Ro 5:5), it would be impossible for them to comprehend the exceeding riches of the love of Christ. This is the climax of prayer, the point to which the other petitions tend. Indeed, from the beginning of the Epistle, he has been declaring what love Christ has shown for the Gentile world.

Wesley's Notes

3:18 That being rooted and grounded - That is, deeply fixed and firmly established, in love. Ye may comprehend - So far as an human mind is capable. What is the breadth of the love of Christ - Embracing all mankind. And length - From everlasting to everlasting. And depth - Not to be fathomed by any creature. And height - Not to be reached by any enemy.

Jamieson-Fausset-Brown Bible Commentary

18. May be able-even still further. Greek, "May be fully able."

breadth . length . depth . height-namely, the full dimensions of the spiritual temple, answering to "the fulness of God" (Eph 3:19), to which the Church, according to its capacity, ought to correspond (compare Eph 4:10, 13) as to "the fulness of Christ." The "breadth" implies Christ's world-wide love, embracing all men: the "length," its being extended through all ages (Eph 3:21); the "depth," its profound wisdom which no creature can fathom (Ro 11:33); the "height," its being beyond the reach of any foe to deprive us of (Eph 4:8) [Bengel]. I prefer to understand "the breadth," &c., to refer to the whole of the vast mystery of free salvation in Christ for all, Gentile and Jew alike, of which Paul had been speaking (Eph 3:3-9), and of which he now prays they may have a fuller comprehension. As subsidiary to this, and the most essential part of it, he adds, "and to know the love of Christ" (Eph 3:19). Grotius understands depth and height of God's goodness raising us from the lowest depression to the greatest height.

Matthew Henry's Concise Commentary

3:13-19 The apostle seems to be more anxious lest the believers should be discouraged and faint upon his tribulations, than for what he himself had to bear. He asks for spiritual blessings, which are the best blessings. Strength from the Spirit of God in the inner man; strength in the soul; the strength of faith, to serve God, and to do our duty. If the law of Christ is written in our hearts, and the love of Christ is shed abroad there, then Christ dwells there. Where his Spirit dwells, there he dwells. We should desire that good affections may be fixed in us. And how desirable to have a fixed sense of the love of God in Christ to our souls! How powerfully the apostle speaks of the love of Christ! The breadth shows its extent to all nations and ranks; the length, that it continues from everlasting to everlasting; the depth, its saving those who are sunk into the depths of sin and misery; the height, its raising them up to heavenly happiness and glory. Those who receive grace for grace from Christ's fulness, may be said to be filled with the fulness of God. Should not this satisfy man? Must he needs fill himself with a thousand trifles, fancying thereby to complete his happiness?