After the first Passover the Israelites were freed out of slavery in Egypt and began to encamp in the wilderness of Sinai (in the year 1441 BCE; see 1 Kings 6:1; Solomon began to build the temple in 961 BCE.). Exactly four weeks later (see Exodus 19) on Shavu'ot (aka. "Feast of Weeks" or "Pentecost" in Greek) the Torah (Law) was given by God to Moses.Around 33 or 36 CE (1470-some years later) the Messiah fulfilled the Law on Passover. Jesus said, "Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them." -Matthew 5:17 (*note: When you graduate from school or college you have fulfilled your requirements. When you receive your diploma you don't tear it up because you're done with your classes and so abolish it. Your studies mean something to you, but you don't go to class anymore. In the same way, we don't have to follow the Law anymore because Christ fulfilled the requirements to graduate from it. We take what we've learned and move on into life walked in the Spirit.) The Messiah freed us from the Law through His death.
Fifty days ("Pentecost" means fiftieth day) after His death on Passover the Holy Spirit was given in Jerusalem (see Acts 2). If you study the two events associated with Pentecost, the giving of the Law and the giving of the Holy Spirit, they are very similar. One is at Mount Sinai; the other is at Mount Zion (symbolic name for Jerusalem). The people of God had gathered on both events. Fire descended from heaven during both events. There was very loud wind or thunder during both events.But, go back and read Exodus 19 and Acts 2. The two Pentecosts are very different in how the people received the gift of God. During one the people trembled and were afraid so much they disobeyed God when He commanded them to ascend the mountain; during the other tongues of fire rested on the people. During one the people received the Law as a result of their disobedience (see Galatians 3:19); during the other the people received the Spirit because of their faith.
At Sinai, even though God told them to come up the mountain they didn't want to meet with God, but they told Moses to relay what God wanted him to say to them. Instead of communing with the Almighty directly, they settled for a middle-man (see Exodus 20:18-21). This is one of the saddest stories in all of Scripture. For 1470-some years the people were imprisoned to the Law by their disobedience (see Galatians 3:23). Since 33 or 36 CE (the death of Christ), Jews who have still clung to the Law are still in bondage to sin. It's like a prisoner who has been declared free to go still clings to the walls of his cell for fear of the outside world that he has not known for so long. So, since their captivity by the Egyptians after the death of Joseph (around 1805 BCE) the Jews have actually only experienced 50 days of freedom (between Passover and Shavu'ot, 1441 BCE). That's over 3800 years of captivity!
At Zion, the church of God was established. All believers commune directly with God the Holy Spirit. Every Christian gets to be a priest in Zion (see 1 Peter 2:5, 9), not just the Levites after Sinai. All of us get to enter the Temple of God because we are the Temple of God (see 1 Peter 2:5). If you are a believer, praise God this day because you can communicate with the Almighty and no longer need a middle-man.
"For you have not come to what may be touched, a blazing fire and darkness and gloom and a tempest and the sound of a trumpet and a voice whose words made the hearers beg that no further messages be spoken to them. For they could not endure the order that was given, 'If even a beast touches the mountain, it shall be stoned.' Indeed, so terrifying was the sight that Moses said, 'I tremble with fear.' But you have come to Mount Zion and to the city of the living God, the heavenly Jerusalem, and to innumerable angels in festal gathering, and to the assembly of the firstborn who are enrolled in heaven, and to God, the judge of all, and to the spirits of the righteous made perfect, and to Jesus, the mediator of a new covenant, and to the sprinkled blood that speaks a better word than the blood of Abel. ...Therefore let us be grateful for receiving a kingdom that cannot be shaken, and thus let us offer to God acceptable worship, with reverence and awe, for our God is a consuming fire. Let brotherly love continue." -Hebrews 12:18-24, 12:28-13:1