When did the Church begin?
The church began at Pentecost, Acts 2. Peter, as the other Apostles, was given the keys to the kingdom (church) (Mt 16:18-19). Peter used these keys to "unlock" the door of the kingdom telling people
how to enter the kingdom (Acts 2:38) to the Jews first in Acts 2 and then the Gentiles (Acts 10:47-48). Those obedient in submitting to water baptism (saved) were added to the church, (Acts 2:47), the body of the saved (Eph 5:23).
"THOSE THAT WERE SAVED"-Seeing that the Church is purchased with the blood of Christ (Acts 20:28); and the blood of Christ is associated with the remission of sins (Matthew 26:28); and baptism is for the remission of sins (Acts 2:38); it makes perfect sense that the Lord immediately adds to the Church (the blood bought body) those who accept the gospel and are baptized (come into contact with the benefits of Christ's death)." Dunagan Comm.