You remember I stated above that when Jesus was baptized by John the Baptist the Holy Spirit descended on Him. Also, before His death Jesus promised to send the Spirit, whom He called the Comforter, to guide and give power to His apostles in their service after His ascension to heaven . Accordingly, ten days after Jesus ascended to heaven , the Holy Spirit was poured out from heaven on all the believers, In power they gave Christ's message to men, and hundreds believed on Jesus Christ. Who is this Holy Spirit? Some have thought the Holy Spirit was the angel Gabriel, or else a prophet. Others have supposed the Spirit was merely a holy influence. However, from the Bible, we see that the Holy Spirit is not one of God's creatures (created beings), but is the Spirit of God, and is one with God. This becomes evident when we take note of what the Spirit does.

Jesus once told a learned man named Nicodemus that he must be born again in order to enter God's kingdom. When Nicodemus asked in surprise how a man who is old could be born a second time, Jesus replied that the new birth is the work of the Spirit. It is evidence that as only God can create physical life, so only God can give men spiritual life and make them new beings. When men live in sin they are children of the devil, but God is able to change them by His Holy Spirit, and when they are born again they become children of God.

Also, the Holy Spirit is the author of God's holy books for it was He who taught and guided the Old Testament prophets like David and Isaiah.  Likewise, it was the Holy Spirit who guided Matthew and Luke and Paul and the other writers of the books of the New Testament for, as the Bible says: "No prophecy ever came by the impulse of man, but men moved by the Holy Spirit spoke from." (2Peter 1:21). Just as God's Spirit guided those who wrote the holy books so the Spirit is the only perfectly true guide of those who read them. Jesus Christ said: "But the Counselor, the Holy Spirit, whom the Father will send in my name, He will teach you all things, and bring to your remembrance all that I have said to you." (John 14:26).

Read more here: Who is The Holy Spirit? - An Explanation Of The Holy Spirit For Muslims