About 3,000 people responded to Peter's sermon on the Day of Pentecost. They listened intently, and due to God's inspiration of Peter's message, drawn entirely from the Old Testament, linking Jesus personally to the events mentioned in the sermon, they responded. They were, in a way, reliving prophesied events that were vitally important as a foundation for their times and most especially, for their nation's future and ours.
However, the newest converts were still not as spiritually well-prepared as the apostles, not having had the advantage of the close companionship the apostles had had with Jesus during the three-and-a-half years of day-and-night experience with Him. Nonetheless, despite the intensity of the activity on the Day of Pentecost and the rising persecution of the church by the Jews that followed, each person called into the church received the Father's careful scrutiny. He was not calling them to failure. Their calling was not a wild scramble to see who might grab the fabled brass ring. From God's point of view, everything is done in love and given due deliberation, so He therefore does everything judiciously.
The apostles moved rapidly to organize the people into local congregations so the called would have as much contact with them as possible. They wanted to ensure that, through Sabbath sermons and Bible studies, they could teach God's way most efficiently. Jesus essentially followed this procedure, and the apostles imitated Him.
What subjects dominated this early teaching? Since the apostles alone were truly close to Jesus, they likely began—as Peter did in his Pentecost sermon—with His personal fulfillment of the Old Testament prophecies, adding that He was their Creator as well as their Savior and King. Even as a human being, Christ was literally God in the flesh, and though He was now at the right hand of the Father in heaven, by faith they were to answer to Him and give Him their loyalty. It makes sense that this would be among the first thoroughly covered teachings to firmly establish His importance to their salvation and the outworking of God's purpose.
They would also pass on to them what they had witnessed of how He conducted Himself during the time they were with Him. Like us, they would have desired to know about His personal characteristics, including His way of dealing with the apostles as well as with the ordinary “man on the street” regardless of the reasons and attitudes of those who came into His presence.
They surely must have studied into the fact that He was the God of the Old Testament, the LORD, the One who personally entered into the covenant with Abraham, the human father of Israel. He was the One who dealt with Moses and the Israelites in Egypt and at Mount Sinai, making the Old Covenant with the descendants of Abraham. This teaching would naturally lead to studies about the gospel of the Kingdom of God and the ongoing creative labors of the Father and Son, who are making sons and daughters in Their image.
This study would lead to a major area of life-changing instruction. Following the coverts' baptisms, each of them, upon receiving the Holy Spirit, became a vital part of the spiritual Body of Christ. They would need to know their behavioral responsibilities as sons or daughters of God.
Most of the early converts were not being called to duty on the front lines, that is, to preach the gospel to large crowds as the apostles did. God was calling them to support the apostles by continuing their personal growth in the grace and knowledge of Jesus Christ and by making a witness through their conduct in their communities. Thus, the apostles would have addressed Christian behavior early. Their personal witnesses were important to the ongoing process God directed through Jesus Christ, though on a narrower scale than that of the apostles.
John W. Ritenbaugh
Why Hebrews Was Written (Part Four)