I know the Holy Spirit came after Jesus resurrection. Some people call it our conscious.
At any rate, Pete then gave a great speech about God’s plan for salvation of mankind. He traced the predictions of the ancient prophets and explained how they pointed to Jesus as the Messiah. Peter reminded them of the wonders and signs, which proved Jesus was God. He showed them the crucifixion was necessary for the forgiveness of their sins. The evidence was overwhelming, an about 3000 people made a decision to believe in Jesus.
This ragtag group turned into a major news story and then into a movement. Jesus had told them to go into the world with his message. With the Holy Spirit power it became possible.
The followers of Jesus became “Christians”. Each known group became known as a “Church”.
Hope that helps you out.
Was this before or after the King James Bible was published?
Actually, when a letter was written to a particular “group” or city it was addressed to “The Church in....”.
From the beginning there was one body, one faith.