The withdrawal of the visible Christ and the substitution of His visible presence in the Paraclete whom He sent was the introduction of His disciples into a higher school of faith. Hitherto they had walked chiefly by sight. The Miracles of their Master had appealed to their reason through the senses. They were not entirely destitute of faith, else they would not have forsaken their fish-nets and followed the Man of Nazareth. But their faith was weak; it needed to be exercised and developed by struggles in a far different arena. They must be taught the spiritual nature of Messiah's kingdom. The visible presence of Christ as a veritable man had been a help to the primary lesson they had already learned; it would be a hindrance to the advanced lesson now to be learned. They must learn that deliverance from sin and restoration to true holiness consist not in outward ceremonials and prescribed rituals, nor in abstract truths grasped by the intellect, but in a vital union with a personal Saviour effected by the Spirit. While Jesus sat there before them in the body the mystery of this spiritual union was altogether beyond their comprehension. The enigma could be explained only by His removal. "It is expedient for you that I go away." This expediency is strongly stated by Draseke as quoted by Stier:
The old Messiah in the flesh is with them; therefore the new Comforter, the Spirit, is far from them. What hindered their being comforted? Jesus Himself, who, comforting, stood before them, was the hindrance. As long as He, this Messiah, bearing all the prophetic marks upon Him, stood before them in person, this, His person continued to be a foundation and prop to that system of vanities which bewitched their heads and hearts, The form must pass away from their eyes before the Spirit could enter their souls. It was good for them that Jesus should go away. Before He, the Christ after the flesh, went away, the Christ after the Spirit could not come. When the former vanished the latter appeared.
The visible, tangible Messiah was the false foundation of all their erroneous notions about a splendid worldly kingdom. The ascension of Christ, the removal of His human form from the eyes of His disciples, was necessary to initiate a purely spiritual kingdom, the basis of which is faith in a risen and invisible Messiah enthroned in heaven. For the same reason the bodily absence of Christ will continue till He descends to judge the quick and the dead and terminate the probationary history of mankind on the earth. His reign as a visible king for a thousand years would be a long step backward. It would destroy the conditions of the development of that stalwart faith which Christ has pronounced specially blessed: "Blessed are they that have not seen and yet have believed."
Again, it was expedient for Jesus to substitute for His visible presence the invisible Comforter for the emancipation of the Jews from "the letter that killeth" — a complex ritual which they had for more than fourteen centuries obeyed with a mechanical precision. This altar ritual, chiefly of bloody sacrifices typifying the atonement in Christ's death, had accomplished its purpose and should now be laid on the shelf as one of "the beggarly elements" — a rudimentary and preparatory dispensation. Also the burdensome law of ceremonial purity, must now be abrogated because it had become a yoke upon the neck of an unspiritual people.
How can this ingrained hereditary worship of "the letter that killeth" all joyful freedom of service be done away without destroying the religious spirit? Christ herein exhibits divine wisdom. He enforced no ceremonial law, nor did He formally abrogate any. But He inculcated the true spirit in which that law should be administered while the Mosaic dispensation should continue. He did not command fasting, but corrected its disgusting ostentation, while intimating that it was not in harmony with His joyful gospel, but, rather, as incongruous as a new patch on an old garment (Matt. ix. 15-17, Revised Version). He did not abolish bloody sacrifices, but prescribed the spirit of reconciliation in which they should be laid upon the altar. He knew that faith in His atonement would supersede the altar ritual without its formal repeal. He did not re-enact the law of tithes, but He insisted that while it continued it should be accompanied by justice, mercy, faith and love. He sought to enthrone in all hearts supreme love to God as the sum of all duties toward God. Then He sends down the Spirit of love, who sheds abroad the love of God in the heart. This inspiration of the evangelical Spirit gradually overcomes the spirit of bondage to the letter, the legal spirit, first in Stephen, then in Saul of Tarsus, and then in the whole Gentile section of the Church, and finally in Peter and the believing Jews. Thus the whole Levitical law is quietly laid aside without a convulsion destructive of faith in revelation. To accomplish this amazing change it was necessary that the God-Man should retire and the God-Spirit should be His successor.
— The Gospel of the Comforter, Chapter 10.