How did the Jews with Peter know the Gentiles had become believers?
The Holy Spirit came down and signified to those seven Jews that the Gentiles had become believers. This happened while Peter was still preaching, before any repentance or baptism, as the Gentiles evidenced salvation by faith alone, not yet Paul's gospel.
Les explains that Peter and six other Jewish believers went to the Gentile home of Cornelius. While Peter had not even finished preaching or mentioned repentance and baptism, the Holy Spirit came down and signified to those seven Jews that the Gentiles had become believers. This happened without an invitation, walking an aisle, repenting, or baptizing; Peter was stopped in his tracks as these men evidenced salvation by faith alone, not yet Paul's gospel, only that Jesus was the Christ.
And they of the circumcision which believed were astonished, as many as came with Peter, because that on the Gentiles also was poured out the gift of the Holy Ghost.
And as I began to speak, the Holy Ghost fell on them, as on us at the beginning.
More Questions
What happened to the circumcised Jewish believers with Peter in Acts 10:45 when the Holy Spirit fell on the Gentiles?
The six circumcised Jewish believers who came with Peter were astonished when they saw the Holy Spirit falling on the Gentile listeners, even though they already believed that Jesus is the Christ.
How many Jews went with Peter to Cornelius, and who were the ones astonished?
According to Acts 11, six Jews went with Peter, so the seven Jews of the circumcision who believed were astonished at what happened.