"The fellowship of thy faith" is capable of more than one meaning. The signification of the principal word and the relation expressed by the preposition may be variously determined. "Fellowship" is more than once used in the sense of sharing material wealth with Christ's poor, or more harshly and plainly, charitable contribution. So we find it in Romans xv. 26 and 2 Corinthians ix. 13. Adopting that meaning here, the "of" must express, as it often does, the origin of Philemon's kindly gifts, namely, his faith; and the whole phrase accords with the preceding verse in its view of the genesis of beneficence to the brethren as the result of faith in the Lord.
The Apostle prays that this faith-begotten practical liberality may become efficacious, or may acquire still more power; _i.e._ may increase in activity, and so may lead to "the knowledge of every good thing that is in us." The interpretation has found extensive support, which takes this as equivalent to a desire that Philemon's good deeds might lead others, whether enemies or friends, to recognise the beauties of sympathetic goodness in the true Christian character. Such an explanation hopelessly confuses the whole, and does violence to the plain requirements of the context, which limit the prayer to Philemon. It is _his_ "knowledge" of which Paul is thinking. The same profound and pregnant word is used here which occurs so frequently in the other epistles of the captivity, and which always means that deep and vital knowledge which knows because it possesses. Usually its object is God as revealed in the great work and person of Christ. Here its object is the sum total of spiritual blessings, the whole fulness of the gifts given us by, and, at bottom, consisting of, that same Christ dwelling in the heart, who is revealer, because He is communicator, of God. The full, deep knowledge of this manifold and yet one good is no mere theoretical work of the understanding, but is an experience which is only possible to him who enjoys it.
The meaning of the whole prayer, then, put into feebler and more modern dress is simply that Philemon's liberality and Christian love may grow more and more, and may help him to a fuller appropriation and experience of the large treasures "which are in us," though in germ and potentiality only, until brought into consciousness by our own Christian growth. The various readings "in us," or "in you" only widen the circle of possessors of these gifts to the whole Church, or narrow it to the believers of Colossae.
There still remain for consideration the last words of the clause, "unto Christ" They must be referred back to the main subject of the sentence, "may become effectual." They seem to express the condition on which Christian "fellowship," like all Christian acts, can be quickened with energy, and tend to spiritual progress; namely, that it shall be done as to the Lord. There is perhaps in this appended clause a kind of lingering echo of our Lord's own words, in which He accepts as done unto Him the kindly deeds done to the least of His brethren.
So then this great prayer brings out very strongly the goal to which the highest perfection of Christian character has still to aspire. Philemon was no weakling or laggard in the Christian conflict and race. His attainments sent a thrill of thankfulness through the Apostle's spirit. But there remained "very much land to be possessed"; and precisely because he had climbed so far, does his friend pray that he may mount still higher, where the sweep of view is wider, and the air clearer still. It is an endless task to bring into conscious possession and exercise all the fulness with which Christ endows His feeblest servant. Not till all that God can give, or rather has given, has been incorporated in the nature and wrought out in the life, is the term reached. This is the true sublime of the Christian life, that it begins with the reception of a strictly infinite gift, and demands immortality as the field for unfolding its worth. Continual progress in all that ennobles the nature, satisfies the heart, and floods the mind with light is the destiny of the Christian soul, and of it alone. Therefore unwearied effort, buoyancy, and hope which no dark memories can dash nor any fears darken should mark _their_ temper, to whom the future offers an absolutely endless and limitless increase in the possession of the infinite God.