At seventy-eight verses, this episode is the longest single episode in the book of Acts.  It is second in importance only to Acts 2, the Day of Pentecost.  Everything changes in this section.  Back in Acts 8 we see the gospel received by a Gentile, the Ethiopian eunuch, but Dr. Luke does not treat this as a critical opening to the Gentiles as a whole.  That comes here in this section with Peter’s work northwest of Jerusalem in Caesarea with a Roman centurion named Cornelius.  But first Peter must be taught by a revelation from God.  What happens is nothing less than a Gentile Pentecost, the Holy Spirit falling on them “just as they did on us [the Jews] in the beginning [Acts 2].”