@abd alrahem,
In John 14:17 Jesus said this about the Paraclete, "You know him, for he dwells with you and will be in you." The Paraclete was already present but his coming would bring about a new relationship with the disciples. He would be
in them rather than just
with them. Beginning at Pentecost the Holy Spirit baptizes every believer into the body of Christ and then dwells within him. This was not true before Pentecost.
The Holy Spirit inspired the followers to write the New Testament. If you read the book of Acts you will see that it took time for them to grasp the meaning of all that Jesus had taught. For example it took a vision from God to convince Peter that he should preach the gospel to Gentiles. But all of this truth was eventually revealed to those who were listening to Jesus.
Where did Jesus say this would happen
before the Paraclete came? In fact Muslims are often among those who kill Christ's followers and think that by doing this they are serving God.
The Holy Spirit is still present in the world in those who believe in Christ while Muhammad is dead.