In the book of Acts, chapter 2:47, it reads: “…And the Lord added to the church daily such as should be saved.” Here Peter was preaching to the men of Israel on the day of Pentecost. The word ἐκκλησία, translated here “church” means a group of people. This assembly consisted of Jews who believed that Jesus was the Messiah. This is the “church” Jesus spoke of in Matthew 16:18 where He said: “upon this rock I will build my church; and the gates of hell shall not prevail against it.” This is not the Church, the body of Christ. It is not the Roman Catholic church. Neither the Lutheran nor Methodist nor Reformed churches. It is Jewish believers of the kingdom gospel. That Jesus is their King and will set up His earthly kingdom. They repented and were baptized. These were not the Jews who came to Christ by hearing the gospel of grace that Paul preached. They are two different groups, and unless we understand this, the Bible will not make much sense. This is why so many church denominations are in error. They mix Israel with Christianity; Paul with the gospels. They teach that Jesus preached to both Jews and Gentiles and that the Twelve taught everyone, as well as Christians. They did not. Jesus said He came only for the lost sheep of Israel and He instructed the apostles to do the same. Jesus preached repentance, water baptism, keeping the Law, forgiving others, and faith in who He was as necessary for salvation. This is not Christianity which teaches faith alone in Christ alone for salvation. The apostles were not Christians. They were Jewish believers who still kept the law.
Sadly. a lot of Christians think that Paul was the 13th apostle. This makes no sense either. Why would God need one more? Besides, Jesus told the Twelve that they would be ruling the 12 tribes of Israel one day. Israel has an earthly inheritance, not a heavenly one. If Peter, the other eleven apostles and Paul were all teaching the same thing, then why did Peter say that Paul’s writings were hard to understand? Why does the Bible say that the Twelve were the apostles of the circumcision (Jews) and that Paul was the apostle of the uncircumcision (Gentiles)? If Paul was chosen to carry out the Great Commission, then why didn’t he go straight to Peter or the other apostles to learn from them? Why was Paul taught by no man but the ascended Christ? And what about the “mystery” that Paul mentions? That secret God kept hidden since the beginning, that Gentiles could find salvation apart from Israel. That they would not be under the law. That God was now extending grace to all who will believe on the Lord Christ Jesus. That Jews no longer needed to be circumcised in order to be saved. That they did not have to perform any works, abstain from any food, observe Feasts days, or sacrifice animals in order to cover their sins. The only requirement for eternal salvation was to believe that Jesus died for their sins and on the 3rd day rose again. Paul taught that. The Twelve never did. This is the message of the cross.
So when exactly did the Christian church begin? It began with Paul in the middle of the book of Acts. In chapter 15 we read about the Jerusalem Council where the apostles, elders and other Jews were assembled, as were Paul and Barnabas, Paul’s companion. Some of the sect of the Pharisees arose and had insisted that Gentile believers needed to keep the law of Moses. Paul argued against them. Finally Peter, who had been silent, stood up and said that through the grace of the Lord Jesus Christ, both Jews and Gentiles shall be saved in the same way. Not long afterwards, it was the Gospel of the grace of God, Paul’s gospel, that was being preached. No more was water baptism being taught as necessary for salvation. But faith in Christ’s finished work on Calvary was and still is.