I have much more to say to you, more than you can now bear. But when he, the Spirit of truth, comes, he will guide you into all the truth. He will not speak on his own; he will speak only what he hears, and he will tell you what is yet to come. (John 16:12-13)
Jesus had been with the disciples for three years, teaching and training them, yet there was still much more they needed to learn. But now there seemed to be two problems. First, they were not yet ready to learn what else Jesus wanted them to understand. Second, Jesus would soon be going away, ascending to his throne at the right hand of the Father.
This would indeed have been a problem, except that Jesus promised that the Spirit of God would now come to be in the disciples as well as with them. And now Jesus himself would likewise be in them as well as with them — through the Spirit (see Ascension and Pentecost). The Spirit would be a paraclete. Paraclete is a Greek word that is variously translated as Advocate, Helper and Comforter. And now Jesus calls him the “Spirit of Truth.” The Spirit of God who would soon come upon them would guide them the rest of the way, leading them into all they would need to know. He would show them the truth.
Today, we almost always think of truth in propositional terms, and there is certainly a propositional aspect to the truth about Jesus the Messiah. However, the New Testament understands truth to be a person — Jesus himself. Earlier, Jesus said, “I am the way and the truth and the life. No one comes to the Father except through me” (John 14:6). He does not simply show us the way — he is the way. He does not merely bring us life — he is life. He does not just teach us the truth — he is the truth.
When the Holy Spirit guides us into “all the truth,” then, it is all about Jesus. Indeed, he reveals to us Jesus himself. That is why the Holy Spirit does not speak on his own, independently of the Lord Jesus. He speaks only what he hears and tells us the things Jesus wants to say to us. That is the same way Jesus himself operated. Jesus did only what he saw the Father doing (John 5:18), exercised no judgment independently of what the Father judged (John 5:30), spoke only what the Father told him to say (John 12:49-50). The Father, Son and Holy Spirit are always in agreement.
Jesus also said that the Spirit would tell of what is to come. It is unclear exactly what this refers to. Perhaps prophetic understanding in general. Perhaps revelatory understanding about the things the disciples themselves were about to see and experience. Perhaps the many things Jesus still had left to teach them, unfolding for them in the days ahead, revealed to them, and through them to us in the Scriptures. The overall point is that the Church will never be at a loss, for the Spirit is always here to help us understand.