Larry Miles gives as one of the five reasons that the church grew in the first century: The Early Church was a Praying Church:
After Peter and John had been released by the Sanhedrin they went back to the rest of the apostles and fellow believers to give a report o what had transpired. Verse 24-31 record that the early Church was a praying church. In Acts 4:29 we read: “Now, Lord, look on their threats, and grant to Your servants that with all boldness they may speak Your word,” They believed in the power of prayer and also of answered prayer. Many of the great figures of the Old and New Testament were people of prayer. God has told us to pray. If we pray, knowing that God hears, and expecting that God will answer in a way that will bring glory to His Name, we can have a victorious prayer life. Remember, it is our Creator that we are talking to. If we can recapture the prayer life of the early church we can better stimulate church growth.
—Larry Miles, “Five Reasons the Early Church Grew (Acts 4)”