After the people gladly received Peter's word in
Acts 2 and obeyed it, counting themselves among those whom Jesus prayed for in
John 17:20 as people who'd believe on Him through the apostles' word, we read the following:
Acts 2:42 And they continued stedfastly in the apostles’ doctrine and fellowship, and in breaking of bread, and in prayers.
They continued in the apostles’ doctrine. Oh that this were the popular trend today! These people followed the doctrine of the apostles as Paul and John urged people to do. They were safe! They did what they had to do.
How many scriptures did we read about our need to continue in the apostles’ doctrine and nothing less?
Why did Luke phrase it in the way he did? Why did he distinguish those who continued in the apostles’ doctrine as, “They that gladly received his word”? It was because not everyone who heard Peter obeyed his word that day. Yes, three thousand did. But, still, not everyone did. And it’s the same today. People will hear this and not gladly receive it enough to obey it.
Peter said, “…every one of you,” when he referred them to baptism in Jesus’ name. He didn’t merely command it, but doubly stressed it by insisting each and every individual be baptized.
This was precisely how we believe on Jesus by the apostles’ words.
After Jesus prayed about everyone believing on Him through the word of the Apostles, we read of nothing preached exclusively by them until Acts Chapter 2. The very day the Spirit was poured out was the first time the Apostles preached after Jesus commanded them to teach people about repentance and remission of sins in His name.
Jesus instructed the Apostles to wait for the promise of the Father before they would proceed to minister that message. The narrative of Acts Chapter 2 has Peter no sooner having finished preaching that message, than the narrative noted the three thousand who responded continued stedfastly in the Apostles’ doctrine.
This informs us the Apostle’s doctrine was established and considered so after merely one message preached in Acts Chapter 2. That message was given in answer to people who wanted to know what they must do upon hearing of the death, burial and resurrection of Jesus. It’s the message Jesus specifically told them to preach after having received the Spirit.