Passage
But when the Comforter is come, whom I will send unto you from the Father, [even] the Spirit of truth, which proceedeth from the Father, he shall bear witness of me:
But when the Comforter is come, whom I will send unto you from the Father, [even] the Spirit of truth, which proceedeth from the Father, he shall bear witness of me:
John 15:24 If I had not done among them the works which none other did, they had not had sin: but now have they both seen and hated both me and my Father.
John 15:25 But [this cometh to pass], that the word may be fulfilled that is written in their law, They hated me without a cause.
John 15:26 But when the Comforter is come, whom I will send unto you from the Father, [even] the Spirit of truth, which proceedeth from the Father, he shall bear witness of me:
John 15:27 and ye also bear witness, because ye have been with me from the beginning.
The verse centers on "Spirit", "comforter", "come", "send", "father", "even", "truth", and "proceedeth". It is saying that the verse draws attention to "Spirit" and "comforter", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 25's "But this cometh to pass that the..." into verse 27's "and ye also bear witness because ye...", so "Spirit" and "comforter" belong inside that flow. In John context, the local focus is the identity of Jesus, new birth, eternal life, and belief and unbelief.
A plain takeaway is to answer the verse's own emphasis on "Spirit" and "comforter" with trust shaped by these words, not by a vague optimism outside the passage.