The flow & purpose of Pentecost
Simply, PENTECOST means 'fiftieth' in Greek. It is 50 days since the rock was rolled away, Jesus had risen. He had ascended 10 days prior to Pentecost. Jesus had appeared to over 500 people, ample evidence to His resurrection.
Then Jesus appeared to more than five hundred brothers at one time, most of whom are still alive, though some have fallen asleep. Then He appeared to James, then to all the apostles. (1 Corinthians 15:6)
In keeping with Jesus' promise, first He must go away that the Holy Spirit may come.
I wll not leave you as orphans ... it is for your good that I am going away. Unless I go away the Counselor will not come to you, but if I go I will send Him to you. (John 14:18, 16:7)
Jesus ascends, the Holy Spirit descends. The Comforter/Counselor is amidst us.
All these events are prophesied, and occur on cue. There would be no Christianity today without these events.
The event of Pentecost is described in Acts 2. The apostles were gathered in Jerusalem when a sound like a mighty wind filled the house, and “tongues as of fire” appeared and rested on each of them. Filled with the Holy Spirit, they began to speak in different languages, proclaiming the mighty works of God to Jews from many nations who had gathered in the city.
This miracle showed that the gospel was not meant for one tribe, one nation, or one language. Christ had commanded his apostles to “make disciples of all nations” (Matthew 28:19), and, at Pentecost, the Holy Spirit empowered them to begin that mission.#
Since Pentecost the Holy Spirit is no 'untouchable Holy Grail' ever talked about but never heard of; He is your Comforter and Counselor forever close. Just call to Him, because He is here to be found.
#Italics sourced from Catholic Answers