John 16:7

Nevertheless, I tell you the truth
Christ was truth itself, and could say nothing else; but he makes use of this way of speaking, to raise the attention of his disciples, and to engage their belief of what he was about to say, and of which they were not easily persuaded; which was, that however overwhelmed they were with grief and sorrow, because of his going away from them, a greater truth he could not tell them, than that this would be to their real good and advantage:

it is expedient for you that I go away;
Christ's death here, as in many other places in these discourses of his, is signified by going away, a departure, taking a sort of a journey, such an one as indeed is common to all mankind; death is the way of all the earth, and which Christ took by agreement with his Father; a dark way is the valley of the shadow of death, and so it was to Christ, who went away in the dark, under the hidings of his Father's face; it is a man's going to his long home, and a long journey it is, till he returns in the resurrection morn; though it was a short one to Christ, who rose again the third day. The phrase supposes the place and persons he went from, this world and his disciples; and the place and persons he went unto, the grave, heaven, his Father, the blessed Spirit, angels, and glorified saints; and is expressive of the voluntariness of his death; he was not fetched, or thrust, and forced away, but he went away of himself; and is a very easy and familiar way of expressing death by, and greatly takes off the dread and terror of it; it is only moving from one place to another, as from one house, city, or country, to another; and shows, that it is not an annihilation of a man, either in body or soul, only a translating of him from one place and state to another. Now the death of Christ was expedient, not only for himself, which he does not mention; he being concerned more for the happiness of his people than of himself; but for his disciples and all believers; for hereby a great many evils were prevented falling upon them, which otherwise would; as the heavy strokes of divine justice, the curses and condemnation of the law, the wrath and vengeance of God, and eternal death, ruin, and destruction; as well as many good things were hereby obtained for them; as the redemption of their souls from sin, law, hell, and death; peace; reconciliation, and atonement; the full and free forgiveness of all their sins, an everlasting righteousness, and eternal life. Moreover, Christ's going away was expedient for his people; since he went to open the way for them into the holiest of all, by his blood; to take possession of heaven in their name and stead; to prepare mansions of glory for them; to appear in the presence of God for them; to be their advocate, and make intercession for all good things for them; to transact all their business between God them; to take care of their affairs; to present their petitions; to remove all charges and accusations; and to ask for, and see applied every blessing of grace unto them. The particular instanced in, in the text, of the expediency of it, is the mission and coming of the Spirit:

for if I go not away, the Comforter will not come unto you; but if I
depart, I will send him to you.
The Spirit of God in some sense had come, before the death of Christ; he had appeared in the creation of all things out of nothing, as a joint Creator with the Father and Son; he was come as a spirit of prophecy upon the inspired writers, and others; the Old Testament saints had received him as a spirit of faith; he had been given to Christ as man, without measure, and the disciples had been partakers of his gifts and graces; but he was not come in so peculiar a manner as he afterwards did; as the promise of the Father, the glorifier of Christ, the comforter of his people, the spirit of truth, and the reprover of the world: there are reasons to be given, why the Spirit of God should not come in such a manner before, as after the death of Christ. The order of the three divine persons in the Trinity, and in the economy of man's salvation, required such a method to be observed; that the Father should first, and for a while, be more especially manifested; next the Son, and then the Spirit: besides, our Lord has given a reason himself, why the Spirit "was not yet given, because Jesus was not yet glorified", ( John 7:39 ) ; And the coming of the Spirit as a comforter, and the spirit of truth, was to be through the intercession, and by the mission of Christ; and therefore it was proper he should go away first, in order to send him; add to all this, that if Christ had not gone away or died, there would have been nothing for the Spirit to have done; no blood to sprinkle; no righteousness to reveal and bring near; no salvation to apply; or any of the things of Christ, and blessings of grace, to have taken and shown; all which are owing to the death of Christ, and which show the expediency of it: the expediency of Christ's death for the mission of the Spirit to his disciples, is very conspicuous; for hereby they were comforted and supported under a variety of troubles; were led into all truth, and so furnished for their ministerial work; and were made abundantly successful in it, that being attended with the demonstration of the Spirit and of power.