"In order that ye may be fully able [Alford] to apprehend [R. V.] with all saints." The tense of the verb "apprehend," Ellicott suggests, implies the singleness of the act, as if through the instantaneous perfecting of love, there comes a sudden revelation of God to the soul, in the face of his adorable Son revealed by the Holy Spirit.
This is the highest and most precious knowledge, for the excellency of which Paul counts all things to be loss, prefacing his declaration with a "yea, verily," as if he thought he had made a splendid bargain. This knowledge, which is so personal that Paul seems in the words, "My Lord," to be its exclusive possessor, he now desires only as the common property of "all saints," because he has found out that Christ can give himself entire and undivided to every perfect believer. Blessed paradox! I do not wonder that an old saint in Wales declared that "Jesus Christ was a Welshman, because he always speaks Welsh to me."
When he prays that the believers in Ephesus may be fully able to apprehend (R. V.) with all saints, he hints at the idea of the equal privilege of all, ascribing to the humblest Christian the highest and most precious knowledge (Phil. 3:8.) Thus men at the top of their transfigured natures stand on a level in the democracy of saintship, rather of kingship; for "He made us to be a kingdom, to be priests unto his God and Father." —Rev. 1:6. (R. V.) The distinguishing privilege of the priest is access to God.
The four dimensions borrowed from the relations of space — though there are properly but three — are intended to express that comprehensive knowledge of all essential truths which St. John includes in the anointing of the Spirit, which teaches all things necessary to life and godliness. "And to know the knowledge-surpassing love of Christ." Here we have acutely conjoined contraries purposely devised by the great apostle to show the immense superiority of heart knowledge to head knowledge. Indeed, mental science has no place for the former in its enumeration of man's cognitive faculties. It recognizes only the intellect. This is correct so far as the unregenerate man is concerned, for "spiritual things are spiritually discerned." The love of Christ is a spiritual thing. By these words we do not understand our love to Christ, but a vivid realization of his boundless love to us who evangelically believe.
— Half-Hours with St. Paul and Other Bible Readings Chapter 4.