What does the Holy Spirit have to do with the truth? Everything. So much so, in fact, that He is called “the Spirit of Truth.”
The phrase “spirit of truth” occurs 4 times in the NASB. All are included in the list below, and three of the four refer specifically to the Holy Spirit. A fifth verse (1 John 5:6) is included because of its similarity of expression and reinforcement of the point that the Holy Spirit and the truth are inextricably linked.
John 14:16, 17 – “I will ask the Father, and He will give you another Helper, that He may be with you forever; that is the Spirit of truth, whom the world cannot receive, because it does not see Him or know Him, but you know Him because He abides with you and will be in you.
John 15:26, 27 – “When the Helper comes, whom I will send to you from the Father, that is the Spirit of truth who proceeds from the Father, He will testify about Me, and you will testify also, because you have been with Me from the beginning.
John 16:13, 14, 15 – “But when He, the Spirit of truth, comes, He will guide you into all the truth; for He will not speak on His own initiative, but whatever He hears, He will speak; and He will disclose to you what is to come. He will glorify Me, for He will take of Mine and will disclose it to you. All things that the Father has are Mine; therefore I said that He takes of Mine and will disclose it to you.” – Note that “The Spirit of Truth” is disclosing the One who is the truth (John 14:6).
1 John 4:6 – “We are from God; he who knows God listens to us; he who is not from God does not listen to us. By this we know the spirit of truth and the spirit of error.”
1 John 5:6 – “It is the Spirit who testifies, because the Spirit is the truth.”