When Jesus had still been on Earth he had a lot of talks with his close friends and companions especially during the time shortly before his assassination. Jesus knew that the Jewish authorities were going to kill him. This is why Jesus prepared his friends for the time when he would no longer travel through the town with them. This is what Jesus said to them:
But very truly I tell you, it is for your good that I am going away. Unless I go away, the Advocate will not come to you; but if I go, I will send him to you. When he comes, he will prove the world to be in the wrong about sin and righteousness and judgement: about sin, because people do not believe in me; about righteousness, because I am going to the Father, where you can see me no longer; and about judgement, because the prince of this world now stands condemned. (Johannes 16, 7 – 11 NIV)
With the word “Advocate” Jesus here means the Holy Spirit. This is something most thrilling. Read the first two chapters of the Acts of the Apostles. After Jesus had resurrected from the dead and had gone back to His Father a group of fearful people remained behind who felt horribly sad and lonely.
Then Pentecost came. That had been a Jewish feast where they celebrated that God had given them their law. This is what happened:
When the day of Pentecost came, they were all together in one place. Suddenly a sound like the blowing of a violent wind came from heaven and filled the whole house where they were sitting. They saw what seemed to be tongues of fire that separated and came to rest on each of them. All of them were filled with the Holy Spirit and began to speak in other tongues as the Spirit enabled them. (Acts 2, 1 – 4 NIV)
Jesus had kept his word. He sent the Advocate to his disciples and friends. From then on the lives of the disciples turned upside down. They were no longer afraid. All the more they freely told everybody about Jesus and encouraged people to believe in Him. This also still applies to us today.