Passage
But when he, the Spirit of truth, is come, he will teach you all truth. For he shall not speak of himself: but what things soever he shall hear, he shall speak. And the things that are to come, he shall shew you.
John 16:13 (DRB)
Nearby Context
John 16:11 And of judgment: because the prince of this world is already judged.
John 16:12 I have yet many things to say to you: but you cannot bear them now.
John 16:13 But when he, the Spirit of truth, is come, he will teach you all truth. For he shall not speak of himself: but what things soever he shall hear, he shall speak. And the things that are to come, he shall shew you.
John 16:14 He shall glorify me: because he shall receive of mine and shall shew it to you.
John 16:15 All things whatsoever the Father hath are mine. Therefore I said that he shall receive of me and shew it to you.
Study Lenses
The verse centers on "Spirit", "truth", "come", "teach", "shall", "speak", and "himself". It is saying that the verse draws attention to "Spirit" and "truth", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 12's "I have yet many things to say..." into verse 14's "He shall glorify me because he shall...", so "Spirit" and "truth" 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 "truth" with trust shaped by these words, not by a vague optimism outside the passage.