Jesus referred to the Spirit in three ways. He spoke of Him as the "Comforter," as "the Spirit of truth," and as "the Holy Spirit." Instead of "Comforter" let us employ the English form of the Greek word, Paraclete. He used that term in each one of these declarations, and it is remarkable that these are the only occasions where the word is used in the New Testament, except once when, in the first letter of John, it is used of Christ Himself.
The word Paraclete simply means "One called to the side of." That opens the way for an understanding of the suggestiveness of the word. It is a word quite common in all Greek literature in the sense of an advocate - that is, one who takes up the cause of another and defends it.
We owe the presence of the word Comforter to the Greek Church, which insisted upon it that the great sense of value in our Lord's use of the word was not so much that the Holy Spirit was to come as an Advocate, as that He was to come to console, and in that sense to comfort the souls of the disciples.
The first time our Lord used the word He coupled with it a very simple word, one of those words we are very apt to hurry over when we are reading, but which gives a key to the situation. He said, "I will pray the Father, and He shall give you" - not a Comforter, but "another Comforter." The word another here is of a particular nature and character; it does not indicate a different quality, but a similarity of quality and a distinction of Person. The value of the use of the word another is that it presupposes a previous Comforter; and thus in His use of the word Paraclete, Jesus suggested that His own work in the case of these men might be designated by that term. He had been the Paraclete. He had been the One summoned to their side. He had been with them; they had been with Him; in fellowship with Him they had seen more deeply into the things of God, they had heard the voices with which they had been unfamiliar until He came and spoke to them; in His presence they had known courage and strength; with Him they had felt that they could dare everything; but their trouble was that He was going. Under these circumstances He said, I will send you another Paraclete; another to stand by your side, another to take exactly the same place that I have filled in your lives during these past three years, Another to be the Advocate of God with you. I think if we compare the way in which Jesus used the word Paraclete with John's use of it in his letter, we may be helped to an understanding of its value. John said, "We have an Advocate with the Father, Jesus Christ the righteous." The risen Christ stands as our Advocate with God in the high places of the heavens; and the Spirit dwells with us as His Advocate in the life and service of the earth. As Christ pleads the cause of man in heaven, so the Spirit pleads the cause of God on earth. He is the Advocate.
Adapted from The Teaching of Christ, The Spirit, by G. Campbell Morgan.