Consider the time of the year and how the Jewish Feasts were celebrated. The feast of the Passover was associated, not only with the time of Egyptian Captivity but also associated with a feast of First Fruits for the first (Spring) Harvest. The harvest during the Passover season was the spring harvest of less hardy crops, such as barley. There were three "harvest" related feasts.
From the time of the Passover Feast (what we know understand as the Resurrection of Jesus) there were 7 weeks and one day counted (total of 50 days) until the Shavuot.
We are told that the Risen Christ ministered to his disciples for 40 days during this period of time, and that it culminated with the command that they should "Tarry in Jerusalem". It is at this time in the desert when Moses receives God's Commandments (Torah)...for it is stated that the time is the third month. The first month being when the Passover occurs. Counting forward from First Fruits, seven Sabbaths, brings us into the third month.
Pentecost is the Greek term for Shavuot and is also known as the "Feast of Weeks" in that it is seven weeks (plus one day) after First Fruits, that Shavuot is celebrated. Along with Passover and Sukkot, it is one of the pilgrimage Feasts that were celebrated in Jerusalem, when the Temple was still standing and are ordained by God as Feasts that are to be kept forever.
Within the New Testament writings, the Feast of Weeks is known as Pentecost. The term Pentecost is of Greek origin and simply means 50th. The calculation of Shavuot is seven Sabbaths (49 days) plus 1 day, thus equaling 50 days.
Jeremiah 31:31-34 HNV said:
"Behold, the days come, says the LORD, that I will make a new covenant with the house of Yisra'el, and with the house of Yehudah: not according to the covenant that I made with their fathers in the day that I took them by the hand to bring them out of the land of Mitzrayim; which my covenant they broke, although I was a husband to them, says the LORD.
But this is the covenant that I will make with the house of Yisra'el after those days, says the LORD: I will put my law in their inward parts, and in their heart will I write it; and I will be their God, and they shall be my people: and they shall teach no more every man his neighbor, and every man his brother, saying, Know the LORD; for they shall all know me, from the least of them to the greatest of them, says the LORD: for I will forgive their iniquity, and their sin will I remember no more."
Ezekiel 36:26-28 HNV said:
"A new heart also will I give you, and a new spirit will I put within you; and I will take away the stony heart out of your flesh, and I will give you a heart of flesh. I will put my Spirit within you, and cause you to walk in my statutes, and you shall keep my ordinances, and do them. You shall dwell in the land that I gave to your fathers; and you shall be my people, and I will be your God."
Imagine what the scene during the time of our Messiah, after His resurrection. He spends forty days with His disciples, teaching them of the things pertaining to the Kingdom of God:
"After his death he showed himself to them and gave many convincing proofs that he was alive. During a period of forty days they saw him, and he spoke with them about the Kingdom of God. At one of these gatherings, he instructed them not to leave Yerushalayim but to wait for "what the Father promised, which you heard about from me. For Yochanan [John] used to immerse people in water; but in a few days, you will be immersed in the Ruach HaKodesh! [the Holy Spirit]" [Acts 1:3-5]
The Disciples had witnessed what had just happened on the Feast of the Passover, and had seen the Risen Christ who explained and revealed the meaning of many sacred secrets to them. They were now approaching another Feast Day and were told to "Wait" with the promise that they would be immersed, not in water, but in the Holy Spirit!
Imagine the anticipation leading up to Shavuot...another Feast is to come, what will happen next?
The disciples of Jesus were Jewish believers who had seen the Messiah after His death; He brought God's Word alive to them, teaching of the mysteries that were hidden, regarding the Kingdom of Heaven, and then they see Him as He ascends into the clouds. He specifically instructed them to wait for the promise. They understood the symbol, that they were looking toward the time that was pre-shadowed by the giving of the Law to Moses. They did not yet understand that that very law would be written into their hearts, and not upon tablets of stone.
Then the day comes... They are waiting together, about 120 of them, in the upper room and Jesus keeps His words and sends the Promise of the Father! The very Spirit that was with them, showing the meanings of the Scriptures and teaching them was now in them, given to them, giving them power to declare what had been shown. Peter's insight regarding what had happened came from the Holy Spirit. "This is what the Prophet Joel spoke of..."
Chronology of the Events found in Acts:
When the Church first began in 30AD, it was entirely Jewish, and evangelism of the Gentiles was not considered. It took ~20 years for them to accept the Gentiles into the church without requiring them to fully convert to Judaism. I don't want to insist that it was exactly 20 years, because as far as I know the exact time isn't clear. But we can get a clue by calculating the date of the conversion of Paul.
This can be derived from Galatians 2:1 where he says:
Fourteen years after I went up again to Jerusalem with Barnabas, and took Titus with me also.
Paul had already been to Jerusalem, three years after his conversion, an event which is mentioned in Galatians 1:18. He is counting 14 years after his conversion, not 14 years after his previous visit, since his conversion was the event that made his life worthwhile. If the two periods are added together we get 17 years, giving the impossible result that Paul was converted before Yeshua had been executed and risen again.
The question is - which visit to Jerusalem is Paul referring to, from which he counts 14 years back to his conversion? Was it the Jerusalem Council of 50AD, or was it the earlier visit, in 46AD when he went with relief for those stricken by the famine?
The heated letter to the Galatians, about circumcision, might lead us to believe that he was referring to the Jerusalem Council of 50AD, but there is something here that doesn't make sense. In Galatians 2:7-14, Paul speaks disparagingly of Peter because he was still vacillating over the question of circumcision of the Gentiles. This means the Jerusalem Council had not yet taken place, because at that Council everybody was agreed that circumcision of the Gentiles was unnecessary, including Peter. (Acts 15:7-11).
Paul must therefore have been referring to the earlier visit to Jerusalem in 46AD when Peter was still not convinced. Subtracting 14 years from 46AD we get 32AD as the date for the conversion of Paul. This is a very early date, only two years after the church was founded, but it is quite feasible. (
Date of Paul's Conversion) Peter's vision and his visit to Cornelius could have been at any time between 35 and 40AD.
Peter's vision was an act of Divine providence, because without it the second generation Believers who began preaching to the Gentiles would have been considered outright heretics. The early Jerusalem Believers never had any thoughts of ministry to the Gentiles, who were totally excluded from the church for at least the first five years until 35AD, and maybe the first ten years until 40AD. After that, the Judaising controversy raged for another 10 or 15 years until it was finally settled in Jerusalem in 50AD.
From the day of Pentecost when the church was founded, it took a total of 20 years for them to welcome the Gentiles without hindrance.
Please see:
http://www.annomundi.com/bible/chronology_of_the_early_church.htm
for more information about Chronology.
__________________________________________
It is important to realize that the Book of Acts covers a larger span of time than many Christians today realize. The suggestion that the Holy Spirit stopped after the book was completed or that the Holy Spirit is not relevant for today is based on an idea that the period of time was rather short. Review of the Feast Days, and their significance shows the time frame that we are in - that we (the modern church) is awaiting the final harvest (the Fall Harvest) and the Time of the Latter Rain. Understanding the significance of the feast of Passover and it's relevance to the Resurrection, followed by the Giving of the Law to Moses -- and how that relates to the Gift of the Holy Spirit and how the Law is written on fleshly tablets is vital to understanding the purpose of the Father.
"Greater love has no one than this, that someone lay down his life for his friends. You are my friends, if you do whatever I command you. No longer do I call you servants, for the servant doesn't know what his lord does. But I have called you friends, for everything that I heard from my Father, I have made known to you. You didn't choose me, but I chose you, and appointed you, that you should go and bear fruit, and that your fruit should remain; that whatever you will ask of the Father in my name, he may give it to you. "I command these things to you, that you may love one another.
... "When the Counselor has come, whom I will send to you from the Father, the Spirit of truth, who proceeds from the Father, he will testify about me." - [John 15:13-17, 26 HNV]
"But I say that so long as the heir is a child, he is no different from a bondservant, though he is lord of all; but is under guardians and stewards until the day appointed by the father. So we also, when we were children, were held in bondage under the elements of the world. But when the fullness of the time came, God sent out his Son, born to a woman, born under the law, that he might redeem those who were under the law, that we might receive the adoption of sons.
And because you are sons, God sent out the Spirit of his Son into your hearts, crying, "Abba, Father!" So you are no longer a bondservant, but a son; and if a son, then an heir of God through Messiah." - [Galatians 4:1-7 HNV]