Jesus Christ preached important moral instructions and guidelines for living a godly life to the Hebrew people while He lived on Earth. He was the Gospel and He had a plan for His followers who were living in spiritual darkness to preach the spiritual meaning of His life, death, and resurrection to the entire world. He had an appointed time to be sentenced, beaten, and crucified on a cross. Jesus died, was buried and was resurrected from the dead for the sins of those who loved Him, believed in His sacrifice and obeyed His commandments. To spread His Gospel, it would be preached but not by Jesus who ascended to Heaven, but by men and women who had the Holy Spirit inside them.
When Jesus told His disciples He had to leave them, He said He would not "leave them as orphans." (John 14: 18); He said God would send them "the Helper, the Holy Spirit, in my name. He will teach you all things and bring to your remembrance all that I have said to you." (John 14:26). Jesus had promised His disciples: "You will receive power when the Holy Spirit comes upon you, and you will be my witnesses... to the end of the earth."(Acts 1:8).
Forty days after being raised from the dead, Jesus ascended into Heaven. His disciples were still in Jerusalem, ten days after the ascension, still feeling destitute for the Messiah they knew. Suddenly the Holy Spirit came down dramatic fashion to the Apostles as the "sound like a mighty rushing wind" (Acts 2:2) and "divided tongues as of fire appeared to them and rested on each one of them." (Acts 2:3). All spoke in other languages which caught the attention of Jews from other lands who were close by, celebrating Passover. The Holy Spirit also imparted the mighty power of Scriptural knowledge and God's wisdom to the disciples, so they could go out in the world and spread the Gospel of Christ.
Peter addressed the befuddled crowd in the first Holy Spirit-filled sermon of the Church Age. He quoted Joel 2:28 which described to the last days of the Church Age when the Creator "will pour out" His "Spirit" so that "your sons and your daughters shall prophesy, and your young men shall see visions, and old men shall dream dreams." (Acts 2:17).
On that day, 3000 souls repented of their sins and were baptized with the Holy Spirit's permanent indwelling of God's kingdom (John 14:16). The Holy Spirit provided a tiny glimpse of fellowship in heaven as more and more people gathered sharing kindness and love with one another. The Apostles shared the Gospel of Christ, which became known as the "Way", and even performed many signs and miracles. Day after day, they attended the "temple together and breaking bread in their homes, they received their food with glad and generous hearts, praising God and having favor with all the people." (Acts 2: 46-47).
The disciples Peter and John were taken to stand before the Pharisees after healing a man who was crippled (Acts 3: 1-10). They were asked by what authority did they heal the man. By the power of the Holy Spirit, they spoke with incredible authority and astonishing boldness, although they weren't educated. The disciples said that Jesus Christ had given them spiritual power. But the Jewish council told them not to speak Jesus' name, but they answered they could not obey them, but God (Acts 3: 13-22).
Stephen became another disciple who was prophesying with the Holy Spirit inside him. He also was taken to the council, he stood and boldly told the Temple authorities about the Old Testament prophets from Abraham to Solomon that they were men of God, unlike these Jewish leaders who had "resisted the Holy Spirit" and killed the prophets and, recently Christ (Acts 7: 1-50).
Stephen angered the temple authorities and was stoned by a group of rabbis. One of these zealous rabbis was Saul of Tarsus, who hated Christians and murdered many of them. Saul didn't hesitate to stone Stephen (Acts 7: 54-60). However, Saul became "Paul" the Apostle who was suddenly stopped on the way to Damascus by Christ Himself (Acts 9: 1-19). As a result, Paul became a bold follower of Christ who tirelessly spread the Gospel to as many towns as he could and revisited others to make sure these "churches" were getting along together as individual bodies of Christ.
The Apostle Paul wrote many of the books in the New Testament which were circulated as letters throughout the Christian communities. Many of the towns he visited were named in chapters in the Book of Acts as well as other "testimonies," later called "books" that composed the New Testament.
Thanks to the dramatic conversion of the disciples by the Holy Spirit, during the first century, the "Way" spread rapidly and extensively from Jerusalem and Galilee to Greek-speaking lands close to the Mediterranean Sea and territory that made up the Roman Empire. Many people took up their cross, adopted Christ as their Savior, and adapted their lives to Christ-centered morally sound teachings.
As the next two centuries came and went, the Holy Spirit continued to inspire and teach people of the Way (Christians) despite increasing persecution until the early fourth century when Christianity became a religion free to be practiced by the Roman Emperor Constantine. Finally, by the mid-4th century AD, the gathering of believers in Christ had a legitimate religion.