The Day of Pentecost is the day of Jubilee. Fifty days after the Passover, the followers of Jesus who believed Jesus was the Messiah, the Son of God, were filled with the Holy Ghost with power and fire.  The Holy Ghost can only be received once someone believes Jesus is the Son of God and receives the Holy Spirit unto Salvation.  But ministry should not begin until one receives the Holy Ghost just as Jesus did after He was baptized in water. This signified the baptism of the Holy Ghost which brings the power.  Just as Jesus did not start His ministry until after He received the Holy Ghost from God, the disciples also waited for the baptism of the Holy Ghost to start their ministry.  Jesus had already breathed the Holy Spirit unto Salvation on them prior to the Day of Pentecost.