He is the Spirit who reveals the truth about God. John 14:17
Jesus said to his disciples, ” The words that I have spoken to you, do not come from me. The Father who remains in me does His own work, for I am in the Father and the Father is in me. ”
The Holy Spirit is the third person of God; God the Father, God the Son, and God the Holy Spirit. He was sent as a helper to dwell among the apostles after Jesus had ascended into heaven. They were fearful, discouraged and lost of hope.
Jesus gave them the Holy Spirit to be an advocator to accompany them for his absence so that they would not be left as orphans. He had told them about the Helper, the Holy Spirit, whom the Father would send in his name. The Holy Spirit who is also a teacher would teach them everything and change them from timidity to bravery. To be strong witnesses for Christ and even died for their faith.
When the day of Pentecost came, all the believers were gathered together in one place. Suddenly there was a noise from the sky which sounded like a strong wind blowing, and it filled the whole house where they were sitting. Then they saw what looked like tongues of fire which spread out and touched each person there. They were all filled with the Holy Spirit and began to talk in other languages as the Spirit enable them to speak. Acts 2:1-4
After which, Peter began to preach with boldness and spoke to the crowd and made his appeal to them and with many other words in his sermon. The power of the Holy Spirit worked tremendously and miraculously that about three thousand people were added to the group that day.
Without the Spirit of God, we are as ships without wind.