Christ started His church during His earthly ministry (Matt 18:17) from people converted and baptized by John the Baptist (Jn 1:35-37) and promised that His assembly would overcome the powers of hell from that time to the end of the age (Matt 16:18). Obviously already extant, the church was “added unto” on the day of Pentecost (Ac 2:41, 47) with the conversion of three thousand men. On aside note, the word "church" is used here ONLY in reference to local church, for there is no other church. Universal church doctrine is heresy.
The common idea adopted by universal church adherents that the church started on Pentecost is unbiblical. No verse anywhere states that the church began on that day. Consider some proof of the church beginning in the days of Christ's ministry.
1. The Lord referred to His church twice in the gospels (Matt 16:18; 18:17), without any indication whatever that it did not yet exist.
2. Jesus Christ, the Bridegroom, had the church as His bride before Pentecost (Jn 3:29; cf. 2 Cor 11:2; Eph 5:22-33).
3. “God hath set . . . in the church, first apostles” (1 Cor 12:28), but the Lord appointed the apostles far before Pentecost (Mk 3:13-19; Matt 10:2-4).
4. Christ sang in the midst of the church (Heb 2:12), but His only recorded singing took place at the institution of the Lord’s supper (Matt 26:30)—an ordinance given to the church before Pentecost (Matt 26:26-31; 1 Cor 11:2, 17-34).
5. Before Pentecost Christ was the shepherd/pastor of His church (Jn 10:14), which was already His flock (a term for the church; Matt 26:31; Lk 12:32; Ac 20:28-29; 1 Pet 5:2-3), until He appointed Peter to pastor His first assembly after His resurrection (Jn 21:15-17).
6. Christ's church had a prayer meeting (Ac 1:15-26), a membership roll (Ac 1:15), a treasurer (Jn 12:6; 13:29), baptism (Jn 4:1-2), the Lord’s supper (Matt 26:26-31), church discipline (Matt 18:15-18), the power to bind and loose (Matt 18:17-18), and the Great Commission (Matt 28:18-20) before it was it was “added unto” on Pentecost (Ac 2:41, 47).
7. On the day of Pentecost in Acts 2 the church simply received the permanent indwelling of the Holy Spirit and public recognition as the new institution for the course of the age of grace (cf. Ex 40:35; the tabernacle; 2 Ch 7:1; Solomon’s temple; Ezk 43:4-5; the Millennial temple).
The New Testament Dispensation Began with John the Baptist, Not at Pentecost
So the NT dispensation began with John, not on the day of Pentecost in the book of Acts (Mk 1:1-4; Matt 11:13; Lk 16:16; Matt 11:5; Mk 8:35)—otherwise Jesus Christ did not preach NT doctrine, the apostles--who were obviously saved before the book of Acts (Lk 5:1-10; 10:20; 18:28-30)-- were not Christians, and other equally absurd conclusions follow.
John the Baptist preached about the Deity of Christ (Jn 1:23; Is 40:3), His substitutionary death (Jn 1:29), repentance (Matt 3:2), hell (Matt 3:10-12), Christ’s bride, the church (Jn 3:29; Eph 5:32), etc. He required confession of sin (Matt 3:6) and evidence of salvation (Matt 3:8) before he would baptize people, so he baptized only believers, not infants. He immersed, not sprinkled or poured (Mk 1:5; Jn 3:23; etc), and his baptism pictured Christ’s coming death, burial, and resurrection (Jn 1:31). He had God’s authority to baptize (Matt 21:24-27), just as the local church has that authority today (Matt 28:18-20). The apostles had John’s baptism (Ac 1:22), but were never “rebaptized” when some supposedly different Christian baptism originated—nor were any other converts ever “rebaptized.” When Christ commanded His church to go into all the world, preach, baptize, and disciple converts (Matt 28:17-20; Mark 16:15-16, etc.), He spoke to those who had received John’s baptism and were familiar with no other kind.
The alleged support for a distinction between John’s baptism and Christian baptism in Ac 19:1-7 is invalid. The individuals of Acts 19 were spurious “converts,” not real disciples of John the Baptist. They did not know the Trinity, and so were unsaved (Jn 17:3), for they had never even heard of the Holy Spirit (Ac 19:2), although John preached about Him (Matt 3:11). Their spurious discipleship is indicated by the fact that the plural word “disciples,” (“mathetai”), is non-articular in Ac 19:1—unlike every single one of the 25 other references in the book of Acts to the word (1:15; 6:1-2, 7; 9:1, 19, 26, 38; 11:26, 29; 14:20, 22, 28; 15:10; 18:23, 27; 19:1, 9, 30; 20:7, 30; 21:4, 16).
Paul does not tell these “disciples” that John’s baptism has passed away and Christian baptism has now been inaugurated; he tells them what John the Baptist really said (Ac 19:4), upon which they believed John’s message as expounded by Paul and submitted themselves to baptism (Ac 19:5-7). Note that a truly born-again man with John’s baptism is not “rebaptized” in the immediately preceding context (Ac 18:24-28) — he is simply instructed in the further developments of truth (for the fact that the gospel dispensation began with John does not mean that everything about God’s new method of dealing with people was instantly perfectly developed).
Ac 18:24-9:7 supports, not undermines, the fact that Christian baptism is John’s baptism, which in turn supports the beginning of the church during Christ's ministry.