When Christ poured out his Spirit on the Day of Pentecost, he ushered his "kingdom community" into the age to come. Pentecost is sometimes described as the birthday of the church, but that is not quite accurate.
Far earlier in the Bible the Greek term ekklesia, which our English versions render "church," had been applied to the "day of the assembly" when Israel gathered at the foot of Mount Sinai as Moses received the Lord's covenant on the mountaintop (Deut. 9:10). From that point forward the term appears regularly in the Old Testament to designate the congregation of Israel assembled to worship in God's presence.
When Simon Peter confessed that Jesus was the Christ, the Son of the living God, Jesus himself promised to build his ekklesia, his assembly, his church (Matt. 16:18). Not surprisingly, therefore, in the interim between Jesus' ascension to heaven and his bestowal of the Spirit from his throne at God's right hand (Acts 2:33), we are shown a community of believers "with one accord…devoting themselves to prayer," awaiting the empowering Spirit of God, whom their Lord would soon send (1:4-5, 8, 14).
The Spirit of God applies Christ's redemptive achievement personally to individuals in the mysterious rebirth that draws us to faith, yet his agenda is not primarily individualistic but rather communal. The Father's call and the Spirit's power rescue rebels from wrath for the purpose of incorporating the redeemed into the assembly of the Lord.
The churchly communal focus of the kingdom is evident both in the immediate response to Peter's sermon on Pentecost (Acts 2:37-41) and in the aftermath of that event (2:42-47). As the Word of God "cut to the heart" thousands of Peter's listeners and they asked how they should respond, he answered, "Repent and be baptized every one of you in the name of Jesus Christ for the forgiveness of your sins, and you will receive the gift of the Holy Spirit. For the promise is to you and to your children and to all who are far off, everyone whom the Lord our God will call to himself" (2:38-39).
Their change of heart (repentance) must be attested publicly by submission to baptism in Jesus' name. And thus it was: "So those who received his word were baptized, and there were added that day about three thousand souls" (2:41).
From the core of one hundred twenty who had awaited the Spirit's descent (1:15), the church swelled as thousands took a public stand, confessing allegiance to Jesus the Messiah, whose name laid claim to them in baptism. As in Abraham's day, God spoke his promise not only to repenting and believing adults, but also to their children (see Gen. 17:5-11).
As God had promised to bless all nations through Abraham, now this blessing would reach pagan Gentiles "far off," whom God would call through the gospel. Individuals' transition from death to life, originating in the Spirit's hidden touch (John 3:8), became visible as they joined the community that confessed Jesus as Lord and Christ (Acts 2:36).
Adapted from Dennis E. Johnson, “Word and Sacrament: Making Disciples of All Nations;" "Acts 4: The Community of the Kingdom" Modern Reformation, Jul/Aug 2011. Used by permission.