In Acts 2 we find the next great event following the marvelous things recorded for us in the Gospels. First, there was the incarnation of our Lord Jesus. God became Man for our redemption. Then Calvary, the sacrificial death of our Lord Jesus Christ, when He gave Himself a ransom for all, to put away our sins. Next, the physical resurrection of the Saviour. Now we have Pentecost, the coming of another Person of the Godhead, the Holy Spirit, to dwell in the Church on the earth and to empower believers to carry the message of grace everywhere.
Notice the opening words, "And when the day of Pentecost was fully come, they were all with one accord in one place." But do not make a mistake. Pentecost did not come because they were of single unity and in one place; they were there expecting Pentecost, in obedience to the words of the Lord Jesus Christ. Pentecost was a predetermined epoch in the mind of God and the Word of God. It had been settled from all past ages just when the Holy Spirit was to descend and take up His abode with the people of God on earth. The Lord Jesus had said that the Father would send the Comforter and "He shall take of Mine, and shall show it unto you" (John 16:15). He also said, "Tarry ye in the city of Jerusalem, until ye be endued with power from on high" (Luke 24:49).
The Holy Spirit was to introduce a new dispensation and God had definitely settled the time when that dispensation would begin—the day of Pentecost. If you turn back to Leviticus 23 you learn there of Israel's ecclesiastical or sacred year, with the great festivals that belonged to it, among them the Passover in the spring, foreshadowing the death of our Lord Jesus Christ. Now when Passover came He died; that is, the appointed Passover. He observed Passover on the evening before His death. The Jewish day began with the evening of one day, as we would count, and went on to the evening of the following day; so on the first evening Jesus ate Passover with His disciples, and before the next evening He died, the spotless Lamb on Calvary. "Christ our Passover is sacrificed for us" (1 Corinthians 5:7).
Then if you follow on in Leviticus 23 you will see that on the morrow after the sabbath they were to bring a sheaf of the firstfruits. Now we are told that Christ has been raised from the dead and "become the firstfruits of them that slept" (1 Corinthians 15:20). So just as Passover typified the death of Christ, the firstfruits typified His glorious resurrection.
Again, referring to Leviticus 23:15,16, we read of a "new meal offering" to be offered fifty days after firstfruits. Pentecost really means the fiftieth day, so God had ordained that this feast should be observed in Israel as the type of the beginning of a new dispensation when a new meal offering would be offered to the Lord: "Ye shall bring out of your habitations two wave-loaves … baken with leaven." These typify those who through the death of the Lord Jesus Christ are presented to God a new creation, Jew and Gentile, sinners in themselves but their sins are judged in the light of the Cross of Christ. Therefore Pentecost was the beginning of a new age, that of the church, the Body of Christ.
The same Holy Spirit who came on Pentecost has been working in power ever since, and it is He who enables servants of God to go into all the world and preach the gospel to every creature, for we read, "It shall come to pass, that whosoever shall call on the name of the Lord shall be saved" (Acts 2:21). It is the same "whosoever" that is in John 3:16: "For God so loved the world, that He gave His only begotten Son, that whosoever believeth in Him should not perish, but have everlasting life." So the Spirit of God has come, the Comforter is here and the saints of God have received the Spirit and have thus been baptized into one Body and in the power of the Spirit are called upon to go forth and proclaim the gospel message to the ends of the earth. Have you called upon the name of the Lord? Have you trusted Christ as your own Saviour? Then doubt not, but accept the words of the Holy Ghost Himself, "Whosoever shall call on the Name of the Lord shall be saved."
—Condensed from "The Acts of the Apostles" by A.C. Gaebelein.