Summary: There are estimated to be at least a half billion Pentecostals alive today worldwide. Why is this significant? Why is it important? The answer lies in the life-changing power for ministry that is loosed in Christian believers by the baptism with the Holy Spirit.
Luke 24:47-49 ...repentance and forgiveness of sins will be preached in his name to all nations, beginning at Jerusalem.  You are witnesses of these things.  I am going to send you what my Father has promised; but stay in the city until you have been clothed with POWER from on high.
Acts 1:4-5, 8 ...“Do not leave Jerusalem, but wait for the gift my Father promised...  For John baptized with water, but in a few days you will be BAPTIZED with the HOLY SPIRIT”...  you will receive POWER WHEN the Holy Spirit comes on you; and you will be my witnesses...”
Acts 2:1-4 When the day of PENTECOST came, they were all together in one place....  All of them were FILLED with the Holy Spirit and began to speak in other tongues as the SPIRIT ENABLED them.
•• Why Pentecost? — because (Luke 24:47, 49) the Gospel needs to be “preached ... to all nations ... [with Pentecostal] POWER”.
• Jesus told these well-trained apostles to “WAIT for the gift,” to “stay in [Jerusalem] UNTIL” they had received “POWER from on high”.
• So why Pentecost? Because without it you are lacking the necessary Pentecostal “power from on high”.
Acts 4:29-31 “Now, Lord, consider their threats and enable your servants to speak your word with great BOLDNESS.  Stretch out your hand to HEAL and perform MIRACULOUS SIGNS and WONDERS through the name of your holy servant Jesus.”  After they prayed, the place where they were meeting was shaken. And they were ALL FILLED with the Holy Spirit and spoke the word of God boldly.
•• Another Pentecostal outpouring is recorded. The Lord added more “Pentecostals” to His Church. Why?
• “They were all filled with the Holy Spirit and spoke the word ... boldly.” Pentecostal preaching is typically known for its boldness and exuberance.
• Why Pentecost? Because without it, most of us do not speak boldly ... even are timid.
Acts 9:17-20 ...“Brother Saul, the Lord — Jesus, who appeared to you on the road as you were coming here — has sent me so that you may see again and BE FILLED with the Holy Spirit” ...  AT ONCE he began to PREACH in the synagogues that Jesus is the Son of God.
• King Saul — the Holy Spirit came on him and turned him into a different person (1 Samuel 10:6).
• Are you content with how you are? Then this message is not for you.
• Do you want more power? more boldness? an outbreak of healings, miracles, signs and wonders?
• Then receive your Pentecost (as in Acts 2). Or receive a renewing of it today (as in Acts 4).
Acts 13:50-52...PERSECUTION against Paul and Barnabas, and expelled them from their region.  So they shook the dust from their feet in protest against them and went to Iconium.  And the disciples were filled with joy and with the Holy Spirit.
•• Why Pentecost? Because it may take that to give you joy in the midst of persecution and hard times.
• “Full of the Spirit” —> manifesting the Holy Spirit fruit of joy
• “Full of the Spirit” —> no room for pessimism
• “Full of the Spirit” —> crowds out that which is not of the Holy Spirit.
Ephesians 5:18 Do not get drunk on wine, which leads to debauchery. INSTEAD, be FILLED with the Spirit.
•• Why Pentecost? Because it fills you with God and displaces carnality and worldliness.
• Remember, He is the HOLY Spirit. Being full of Him is a wonderful sanctifying influence. Biblical “Pentecostals” are enabled by the Holy Spirit's infilling to increase in personal holiness.