By being enrolled as one of Jesus' students, and being ruled by what He taught, these first disciples soon discovered that many of their instinctive social customs were at odds with the teaching they had been given. Luke tells how the church took up the challenge, and how they were encouraged to consider the issues that confronted them: if God by raising Jesus from the dead had shown Him to be the Son of Man, then how far did this Sonship extend? What was their place in the ongoing work of the Holy Spirit, by which all the earth would come to hear of God's Salvation?
We can describe Luke's intentions in telling us about Peter's work like this: Peter began to do the work His Master had commanded him to do. Luke gives us a picture of Peter as one who was becoming a shepherd, following the footsteps of the Good Shepherd. As Peter continues this work, at Lydda, then at Joppa, then at Caesarea, he found he was becoming more sensitive to the promptings of the Holy Spirit. He begins to better understand his own experiences as a student in Jesus' school. He begins to grasp Jesus' teaching in new and fresh ways.
Luke reported these events shortly after Saul's conversion telling us about Saul's visit with Barnabas to the apostles in Jerusalem. That the persecution ceased for a time leads us wonder whether Gamaliel's comments to the Sanhedrin (to leave the apostles alone) had been part of a policy in support of Saul's operation against the 'rank and file' members of the church. God's intervention on the road to Damascus seems to have exposed Gamaliel's ruse! From what is here recorded, Luke seems to suggest that first the persecution under Saul's leadership, and then the proclamation of the Gospel by Saul/Paul were a well-known and well-established part of the lives of synagogues in that part of the Meditteranean (9:21 & 29).
Luke was writing a book for those who needed to know, for those who knew part of the story. The followers of Jesus were being formed into a new society by the Holy Spirit Himself, enabling them to face up to, and overcome, long-term inherited practises that had confirmed their separation from each other. But the Holy Spirit was not poured out simply to enable the earliest Christians to devise new customs as Jews and Gentiles welcomed each other. That they did is an amazing fact in itself, but it was all part of an ongoing work directed by the Holy Spirit by which the good news would be told throughout all the earth. The soil will be prepared and the good seed will bring forth a great harvest.
For as the earth brings forth its shoots and as a garden causes what is sown in it to spring up, so the Lord God will cause righteousness and praise to spring forth before all nations.
And what are we to make of "tongues", the amazing sign of God's Spirit being outpoured? Paul later wrote that "tongues are for a sign, not for believers but for unbelievers". This has an important application for how we understand Luke's account of tongues in Acts 2 and Acts 10. It is not that the absence of tongues means a person is still in unbelief, so much as the gift of "hearing tongues" being God's way of impressing upon those who have not understood the wide extent of His grace. The work He undertakes in us will not be limited by ethnic or lingual backgrounds. The creating and renewing power of the Son of God overcame the cultural confusion that had bedevilled human relationships since Babel.