The Spirit of truth is the Spirit of Christ, and below are four ways Scripture reveals this.
1) John 14:16-17, 26; 15:26 reveals the Comforter is the Spirit of truth and the Comforter is Christ. Jesus said, “I will not leave you comfortless: I will come to you.” John 14:18
2) John 14:6 says Jesus is the truth and by His Spirit He is the Spirit of truth. “JESUS saith unto him, I am the way, THE TRUTH, and the life:” John 14:6
3) The Spirit of truth does not speak of Himself; it is the Father that tells “Him” what to speak and that “Him” is Christ. See John 8:28; 12:49; 14:10, 24 and 16:13 below.
4) The Spirit of truth is also to show us things to come which Revelation 1:1 tells us it is Jesus Christ which is once again revealed to Him by His Father.
John 16:13 “Howbeit when HE, the SPIRIT OF TRUTH, is come, he will guide you into all truth: FOR HE SHALL NOT SPEAK OF HIMSELF; but whatsoever he shall hear, that shall he speak: and HE WILL SHOW YOU THINGS TO COME.”
Note that the above verse says the Spirit of truth is a “HE” and that “HE” is “Christ” Himself by His Holy Spirit. Christ is a “HE” even if it is by HIS Spirit!
Note also in John 16:13 above that the Spirit of truth (Christ) does not SPEAK OF HIMSELF but speaks what He hears from someone else. In the verses below we find that someone else is His FATHER.
JESUS DOES NOT SPEAK OF HIMSELF but WHAT THE FATHER INSTRUCTS HIM TO SAY. And that remains the same when Christ returns as our Comforter and Spirit of truth. Even by His Spirit, HE DOES NOT SPEAK OF HIMSELF but speaks WHAT HE HEARS FROM HIS FATHER. That is what He shall speak.
John 12:49 “FOR I HAVE NOT SPOKEN OF MYSELF; but the FATHER which sent me, he gave me a commandment, what i should say, and what i should speak.”
John 14:10 “The words that I speak unto you I SPEAK NOT OF MYSELF: but the FATHER that dwelleth in me,”
John 14:24 “He that loveth me not keepeth not my sayings: and THE WORD WHICH YOU HEAR IS NOT MINE, but the FATHER’S which sent me.”
John 8:28 “When you have lifted up the Son of man, then shall you know that I am he, and that I DO NOTHING OF MYSELF; but as my FATHER has taught me, I speak these things.”
So when Jesus was on Earth, He did not SPEAK OF HIMSELF but what the Father told Him to speak. And when Jesus returned by His Spirit as the Spirit of truth, nothing changed. Jesus by His Spirit does not SPEAK OF HIMSELF but what the Father has shown Him.
The Spirit of truth is also to SHOW US WHAT THINGS ARE TO COME which we find in Revelation 1:1 is also Christ. Just as the words He speaks are from His Father, so are the things to come that He is to show us. And hence we find all Scripture lines up without any contradiction or inconsistencies as truth always does.
Revelation 1:1 “The Revelation of JESUS CHRIST, WHICH GOD GAVE UNTO HIM, to show unto his servants things which must shortly come to pass;”
The Spirit of truth is the Spirit of Christ. Thus the Holy Spirit is NOT a third being but the Spirit of God coming to us through His Son.