Day of Pentecost Fulfills Historical Event of Israel on Mt. Sinai
"And when the day of Pentecost was fully come...there came a sound from heaven" 52 "and they were all filled with the Holy Ghost" 53 and they received "the gift of the Holy Ghost." 54 The disciples had waited fifty days since receiving the Spirit when Jesus breathed upon them, and now had received the gift of the Spirit "upon" them from "on high."
Therefore, we conclude that the first feast of Pentecost after the resurrection was not the official beginning of the ministry of the Holy Spirit on earth, but that He was already present when Jesus breathed upon the disciples. In this sense, the proximity of Passover and Pentecost (being only fifty days apart) is significant.
Jesus said, "Behold, I send (ie. am continuously sending) the promise of my Father upon you." 55 The disciples had received, were receiving, and would receive again the presence of the Holy Spirit as He was poured forth.
It is clear that New Testament Pentecost is related to Israel's Mt. Sinai experience. The disciples in the upper room heard God's voice such as it was "a sound from heaven as of a rushing mighty wind", 56 whereas Israel said, "Let not God speak with us, lest we die." 57 At Mt. Sinal "there fell of the people that day about three thousand men", 58 and at Jerusalem "there were added unto them about three thousand souls." 59
Since the disciples had already received the Holy Spirit, "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." 60 So if we wait for Him, 61 we will experience this outpouring and see the greatness of God because He will do "terrible things which we looked for." 62