The Holy Spirit will come. "When they therefore were come together, they asked of him, saying Lord, wilt thou at this time restore again the kingdom to Israel? And he said unto them, It is not for you to know the times or the seasons, which the Father hath put in his own power. But ye shall receive power, after that the Holy Ghost is come upon you: and ye shall be witnesses unto me both in Jerusalem, and in all Judea, and in Sameria, and unto the uttermost part of the earth.
And when he had spoken these things, while they beheld, he was taken up; and a cloud received him out of sight. And while they looked steadfastly toward heaven as he went up, to behold, two men stood by them in while apparel; Which also said, Ye men of Galilee, why stand ye gazing up into heaven? this same Jesus, which is taken up from you into heaven, shall so come in like manner as ye have seen him go into heaven.
"And when the day of Pentecost was fully come, they were all with one accord in one place. And suddenly there came a sound from heaven as of a rushing mighty wind, and it filled all the house where they were sitting. And there appeared unto them cloven tongues like as of fire and it sat upon each of them. And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance. (Acts 2:1-4)
The Apostle Peter said "But this is that which was spoken by the prophet Joel; And it shall come to pass in the last days, saith God, I will pour out of my Spirit upon all flesh and your sons and your daughters shall prophesy, and your young men shall see visions, and your old men shall dream dreams: And on my servants and on my handmaidens I will pour out in those days of my Spirit; and they shall prophesy: I will show wonders in heaven above, and signs in the earth beneath; blood, and fire, and vapor of smoke." (Acts 2:16 -20)
The Apostle Peter clarified that this baptism of the Holy Ghost was to be a prophecy , a sample, of what was to take place during the Day of the Lord, the tribulation which he desribed.
We would like to emphasize that this baptism of the Holy Spirit at Pentecost, is not the nine gifts of the Holy Spirit, as described by the Apostle Paul in 1 Corinthians 12. The miracle of Pentecost occurred on the fiftieth day after Passover, counting from the second day of the Feast (see Acts 2:1; 20:16; 1Cor.16:8) for divine instructions to Israel. (see Exo. 23:16; 34:22; Lev.23:15-21; Num.28:26-31, Deut. 16:9-11)
The name of the event "Pentecost" in Greek "(#4005) pentekoste, fem. of the ord. of #4004; fiftieth (#2250 being implied) from Passover, i.e. the festival of "Pentecost";- Pentecost. #4004 pentekonta; mult. of #4002; fifty:-fifty. #4002 pente, a prim. number; "five":-five. #2250 hemera, fem.. gentle; day, in example (lit) the time space between dawn and dark.." (Greek Dictionary of the New Testament p.56)
Everyone present was Galilaean. (see Acts 2:9) The languages they received and did not previously know, were ethnic languages, or "dialects." [In other words they were recognized languages, interpreted by those who were visiting in the city from other nations.] (Note KJV p.1356 in ref. to Acts 2:1-13)
The participants were to go all over the world and spread the good news of what they had just witnessed by going to the countries unique to the dialect they had received, so it could be understood directly. There were people in the area from all other nations according to the Scriptures.
What does Pentecost refer to in relation to the Old Testament. A Reference in Exodus 34:22, 23 : "And thou shalt observe the feast of weeks, of the firstfruits of wheat harvest, and the feast of ingathering at the year's end. Thrice in the year shall all your men children appear before the Lord GOD, the God of Israel."
In Leviticus we have the completion of the barley harvest which explains why Pentecost was fifty days after Passover. "And ye shall count unto you from the morrow after the sabbath, from the day that ye brought the sheaf of the wave offering; seven sabbaths shall be complete: Even unto the morrow after the seventh sabbath shall ye number fifty days; and yeshall offer a new meat offering unto the LORD." (Leviticus 23:15,16)
We may be asking what is Passover? It is a Jewish festival commemorative of the exodus from Egypt (to the promised land). It wasn't a coincidence that Jesus was crucified on Passover. The Resurrection, Hades and Pentecost is also related to the "Feast of Harvest" in Exodus 23:16.
Pentecost is the beginning of calling God's laborers out of the field through the resurrection of Jesus Christ. Jesus Christ was the first fruit and the first human body ever to be resurrected. The resurrection began with Him. Bodies came out of graves at this event. "And the graves were opened; and many bodies of the saints which slept arose." (Matthew 27:52)