The Gift of Pentecost.

The Book of the Acts of the Apostles (2:1-7, 14, 38-41)
When the day of Pentecost arrived, they were all together in one place. And suddenly there came from heaven a sound like a mighty rushing wind, and it filled the entire house where they were sitting. And divided tongues as of fire appeared to them and rested on each one of them. And they were all filled with the Holy Spirit and began to speak in other tongues as the Spirit gave them utterance.
Now there were dwelling in Jerusalem Jews, devout men from every nation under heaven. And at this sound the multitude came together, and they were bewildered, because each one was hearing them speak in his own language. And they were amazed and astonished, ...
But Peter, standing with the eleven, lifted up his voice and addressed them, "Men of Judea and all who dwell in Jerusalem, let this be known to you, and give ear to my words." ...
And Peter said to them, "Repent and be baptized every one of you in the name of Jesus Christ for the forgiveness of your sins, and you will receive the gift of the Holy Spirit. For the promise is for you and for your children and for all who are far off, everyone whom the Lord our God calls to Himself." And with many other words he bore witness and continued to exhort them, saying, "Save yourselves from this crooked generation."
So those who received his word were baptized, and there were added that day about three thousand souls.

Homily
Fifty days after Passover (when our Savior was crucified) was another important Jewish holiday when devout Jews would gather in Jerusalem. God chose this Pentecost to pour a new significance to this ancient holiday. He poured out the Holy Spirit onto the believers there in Jerusalem, sparking a spiritual uproar as pilgrims gathered to hear the good news of Jesus Christ from Peter and the other empowered apostles. The wait for the fulfillment of the promise made last week as He ascended was finished in spectacular fashion as the Spirit came upon them with signs and great power. Designed to draw a crowd and teach them that God's promise was to all nations. That includes us.