“But when the Helper comes, whom I will send to you from the Father, the Spirit of truth, who proceeds from the Father, he will bear witness about me. And you also will bear witness, because you have been with me from the beginning.” (John 15:26–27, ESV)
These words may not have meant much to His disciples at the moment. They still did not even understand what was about to happen. But Jesus knew just how important they were and He said them. He knew He was leaving. He knew He was about to be put to death and that this in itself would be a big blow to them. But He also knew He was going to take His life back up again, appear to them, and they leave them again until they met in eternity. All of these things would soon come to pass, and Jesus knew that they needed to hear these words, but more than that they needed to know the truth that they would not be left alone.
They were not being sent alone out into the world to face persecution and rejection while presenting the love of God to men. This was not something that they were to do on their own in remembrance of Him who was once with them. Rather, through the coming of the Spirit they would continue to know Him alive and abiding in them. In the fullness of God’s plan when the Son returned to the Father, the Father sent the Spirit. And while Christ was with them in human form, the Spirit would be in them forever. And as we read in Scripture the Father, Son, and Spirit are fully in each other. They are One.
With Jesus leaving the disciples were promised that God would be fully present in them through the Spirit, and in the Spirit they would be fully helped—enabled and empowered. The disciples, who in a unique way only to themselves, were the ones who were with Jesus. They walked, slept, and ate with Him. They knew Him in a way that no one else did, and when He left they were the ones who could tell of Him to everyone else. They were the ones that God would empower to build His church, and through the power of the Spirit they would be given all that they needed in order to do so. Even the things that they had been told, but did not put the pieces together concerning, the Spirit would bring to their remembrance and shine the light of understanding on. These are the men who would be there at Pentecost when the Spirit came upon all believers. These were the men who would see the initial large numbers of people come to faith in Christ. These are the men who would be the foundation of the church in which Jesus is the chief cornerstone. And these are the men who would write for us the Scriptures that we hold in our hands, as the Spirit moved through them as the Spirit moved through the prophets before.
They personally knew and loved Jesus in a way that no one else could claim, and from them the good news of salvation in Christ alone was to be spread. This is a monumental task, and it is one that was made possible because the Father sent the Spirit to forward what had been accomplished in the Son. These men were truly to be the eyewitnesses that would change the world.
The incredible thing is that the work of the Spirit did not end with them. Every single person who believes and is saved is at that time permanently indwelt by the Spirit and gifted by God for His service. The Spirit continues to open eyes so that people might be saved, and the Spirit continues to grow believers once they are saved. We are vessels chosen by God for His service.