Jesus said in John 16:13-15(ISV), “Yet when the Spirit of Truth comes, he’ll guide you into all truth. He won’t speak on his own accord, but he’ll speak whatever he hears and will declare to you the things that are to come. 14 He will glorify me, because he will take what is mine and declare it to you. 15 All that the Father has is mine. That is why I said, He will take what is mine and declare it to you.”
John 14:16-18 proves that the Holy Spirit of truth who was with the disciples as a man via incarnation, would later be inside the disciples as a new manifestation of the Father’s own indwelling Spirit of truth. Although John 16:13 proves that the Holy Spirit of Christ would not “not speak on His own accord,” but only what “He hears,” from the Father, the indwelling Spirit of truth would also be the Father’s own omnipresent Spirit in a new manifestation that God never had before the ascension of Christ (Ephesians 4:10; 1 Corinthians 15:45). That is why Jesus explained what he meant in the next verse (vs. 14) - “All things that THE FATHER HAS ARE MINE; THEREFORE I SAID that HE (the Father) will take what is mine and declare it to you.”
The Father would glorify the man Christ Jesus because the Father would “TAKE OF MINE” (The Father would TAKE OF Christ’s human spirit of priestly knowledge and intercession) “and declare it to you.” Hence, the things that belonged to the human Son are now made known to Christ’s true disciples through the Father’s indwelling “Spirit of truth” who was with the disciples as a man, but would later be in the disciples as the Father’s Spirit of truth which is Christ. This is precisely why Romans 8:26-27 says, “… the Spirit makes intercession for the saints according to the will of God” (which Romans 8:9 and Romans 8:34 says is Christ). And this is why 2 Corinthians 3:17 says, “The Lord is the Spirit” – “Jesus is Lord” so he is the Spirit. For why else would 1 Corinthians 2:16 say, “We have the mind of Christ” other than having “the mind of Christ” through the indwelling Spirit?