John xv. is not here alleged; because in the teaching of the Vine and its branches the Lord does not set forth our oneness with Himself, but our need of dependence continual on Him in order to bear fruit. The necessity of communion with Him practically is the point, not the privilege of union.
But it is in chap. xvii. where this great truth of family union has its fullest expression. And no wonder; for it is the Son pouring out His heart's desires about His own to the Father before His departure. There are three occasions in our Lord's utterance where oneness is asked for His saints, and each of these has its own distinctive character.
First, in ver. 11 He says, "Holy Father, keep them in thy name which thou hast given me, that they may be one as we." It is for those who then surrounded Him (as is certain from vers. 12, &c.), about to preach, teach, and act with apostolic authority when, Himself gone on high, the new work of God had to see the light as the witness of Christ here below. He is not content with requesting that, as He was taking a new position as the glorified Man in heavenly glory, in virtue of His person and of His work (1-5), they might share it as far as could be, both before the Father (6-13) and before the world (14-21); He asks that in this they might be "one," further adding " even as we." This goes wonderfully far in His demand on the Father. And it was wonderfully answered in that unity of mind and purpose, of word and deed, of heart and service which characterised that holy band. Where and when was there anything to compare with it at any epoch before or since? It is the more striking in the twelve; for we heard of their marked differences, and their mutual jealousies, (alas! how like other saints and other servants of the Lord in all ages), which the presence of the Lord only checked but in no way excluded, as the Gospels faithfully tell us. See the same men when the Holy Spirit was given: how their words and ways by His power only evinced the activities and affections of the life they had in Christ! "Peter standing up with the eleven," they were now truly one. If the multitude of those that believed could be and is said to be of one heart and one soul, and earthly possessions only gave occasion for love, still more emphatically was it true of those "God set first in the church."
Secondly, in ver. 20, 21 the Lord makes request "not for these only, but also for those who believe on him (Christ) through their word." This enlarges the sphere, and embraces the mass of the saints following, who received the gospel in the love of the truth. Here therefore, anticipating the world-wide testimony and its rich results, He says "that they may all be one, as thou father [art] in me and I in thee, that they also may be one in us, that the world may believe that thou didst send me." It is not at all so simple and absolute as in the first case, where divine power wrought to secure an end so all-important. The vast range of their mission was an astonishing witness to the grace that operated in the face of every hindrance, but the effect of the power was attenuated ere long and never so complete. It is the unity of grace, of Christians in the Father and the Son (" one in us "), rising above obstacles within and without through the power of what was revealed and of Him Who made the blessing theirs: to the world, which had known them so different in every way and now beheld them " one," a testimony far mightier than miracles however striking and numerous. And so it runs, "that the world may believe that thou didst send me." For this was what sounded out in every place-that the Father sent the Son as Saviour of the world, themselves its living example in their measure, all prejudice notwithstanding.
Thirdly, " the glory which thou hast given me I have given them, that they may be one, even as we are one; I in them, and thou in me, that they may be perfected into one, that the world may know that thou didst send me, and lovedst them even as thou lovedst me." Here, though the Lord gave the title then, He looks on to the glory and the glory displayed to the world. It is oneness in that day, and is a character without alloy, quite answering to that of the new Jerusalem in Rev. xxi, where the world beholds the glory of the heavenly city, the Bride or Lambs wife; not the mutuality of grace as now, but the order of glory, Christ in the glorified saints, and the Father in Christ. Hence then only will they be "perfected into one;" and then only will the world "know" that the Father sent the Son. For how else could those who were once sinners be in heavenly glory but by His Son sent for their salvation? How else, that the Father loved them even as He loved the Son, but by their manifestation with Him in glory? It is now a question of the world's "believing;" in that day the world will "know," because it will see the glory in which Christ and the church will shine together.