The declaration that it was expedient, or "good," as Luther translates it, for Christ to go away in order that the Comforter might come, proves the fact that the work of the Holy Spirit is so indispensable a complement to His own work that His bodily withdrawal, which is the condition of the Spirit's advent, should awaken great joy in the hearts of His disciples. A few disciples, comparatively, had seen Him in His humiliation, rejected of men; now One was to come who should be a mirror in which all disciples in all lands and in all generations should see Him glorified, and, seeing, "should be transformed into the same image from glory to glory." Without Jesus radiant with divinity, the Comforter would have nothing to reproduce in the heart of the believer. It would be like removing from the photographer's studio the person whose features the sun is about to fix on the plate prepared to receive them.
The radical dissimilarity between the old and the new dispensation is seen in the following particulars: In the old dispensation the Spirit externally wrought upon men, but He did not in His person dwell in believers; His working was occasional and for a short time; He did not permanently abide in them. He was external; He did not incarnate Himself in believers. His action Was intermittent, irregular, and apparently without any law. He came and went like Noah's dove, finding no abiding place. But in the new dispensation there is a "law of the Spirit" by which all believers may receive Him as a permanent dweller in the heart as another dove seen by John the Baptist descending upon Jesus and abiding on Him as a part of His person. In the Old Testament the Spirit bestowed gifts of an intellectual and physical nature — prophecy to the seventy elders, skill to Bezaleel, the kingly feeling to Saul, and strength to Samson. But the Comforter dispenses the various graces, such as saintly inward virtues, love, gentleness, goodness, etc. "Affianced of the soul, the Spirit went oft to see His betrothed, but was not yet one with her; the marriage was not consummated until Pentecost, after the glorification of Jesus Christ."
Another great gain to the disciples in the exchange of the bodily presence of Christ on the earth for His spiritual presence in their hearts, by the Comforter's coming and indwelling, was in the clearer evidence of his Messiahship and divinity. Doubtless the disciples at the first intimation of Christ's intended departure asked of one another, "What proofs can we hereafter point to that we have not followed a pretender if the great miracle worker removes. His amazing miracles have been our chief argument with our enemies hitherto. Nothing can supply their place in even keeping ourselves from serious doubts. What shall we do?" Little could they possibly comprehend that an invisible divine Person could descend from heaven, enter into their very being, pouring a light more resplendent than the sun upon the person of Christ, giving an intuitive perception of His supreme Godhood as indisputable as any self-evident truth of the human reason. They knew nothing of the self-evidencing power of the Spirit to glorify the Son of God in their consciousness and to plant their feet for evermore on the sunlit summit of full assurance and certain knowledge so frequently spoken of by Paul under the strengthened word epignosis.
The death of Christ was deemed by His disciples as the greatest possible disaster, but it redeemed a world of sinners lost. So the departure of their Master was deemed a privation for which they could imagine no compensation, but it removed the barrier which kept Him from access to their inmost selves. Hitherto He had been imprisoned within walls of flesh obstructing the full communication of Himself to their hearts, just as the unbroken alabaster flask kept the delicious perfumes from filling all the house, every crack and crevice, with its pervasive odors.
When the God-Man was on the earth He was farther from His disciples, even when He washed their feet, than the sun is from the earth, 93,000,000 miles away. But when He came in the form of the Comforter this distance was annihilated. The disciples now have an eternal sunrise within their hearts. They are ensphered in the Spirit, who reveals Christ. They are enveloped in His personality; they are "in Christ."
— The Gospel of the Comforter, Chapter 10.