Silas was a Jewish Christian who appears to have been active in the Jerusalem church, assuming that the Silas mentioned in 15:22 is the same man (see Witherington, Acts, 473.). That Luke should mention a character in one context then pick him up again later is a common feature of the book.
Silas is likely an Aramaic form of the name Saul. The Silvanus of 1 Peter 5:12 is likely the same man since Peter would have know Silas from Jerusalem. Silas is mentioned frequently in Paul’s letters, 2 Cor 1:19, and he is a “co-sender of the Thessalonian letters (1 Thess 1:1 and 2 Thess 1:1). It is therefore suggested that he functioned as a secretary for Paul in the writing of these letters (and perhaps others). 1 Thess 2:6 refers to the “apostles of Christ,” which may imply that he was considered an apostle like Barnabas, although not from the Twelve.
Silas was a Roman citizen since Acts 16:37 implies that he was imprisoned illegally. This would seem to imply he was a Hellenistic Jew. His name confirms his: he is also known as Silvanus, a Roman cognomen meaning “wood,” and the same name as the Roman god Silvanus, a life-giving deity (Gillman, “Silas,” in ABD 6:22).
He traveled with Paul for most of the second missionary journey. In Acts 17 he and Timothy returned to Berea and Thessalonica while Paul continued on to Athens and Corinth. R. C. Campbell suggests that since Silas was able to return to these locations indicates that Silas was “less controversial” than Paul (ISBE Rev, 4:509). This might be true, but it may be that Silas was more acceptable to the Jews socially and theologically than Paul. What is remarkable is that after he joins Paul in Corinth, he drops out of the story.
B. N. Kaye suggested that Luke used Athens and Corinth to signal a shift in Paul’s strategy: “Luke is pre-occupied with the re-direction of Paul’s mission from the synagogue where it is directed towards the Jews, to a house where it is directed explicitly, though not exclusively, to the Gentiles” (25). This shift to the Gentile mission in Corinth receives a confirmation when Paul is vindicated in court before Gallio. I would add that Corinth is Paul’s most successful church up to this point in Acts, although there are a host of problems associated with non-God-Fearing Gentiles coming to Christ.
So why Silas? Like Barnabas, he was a Hellenistic Jew yet he was firmly rooted in the Jerusalem church. Paul seems to have wanted a companion who was “acceptable” to Jerusalem, perhaps to preempt any criticism of his Gentile mission by the more conservative elements of the Jerusalem church. Paul would therefore represent the Antioch churches, Silas the Jerusalem churches, implying that any mission to the Gentiles was co-sponsored by both centers of Christianity. Does Silas depart after Paul makes his declaration in the synagogue in Corinth? We cannot know for sure, but it is possible this he he reacted against Paul’s turn to the Gentiles, similar to John Mark after the incident on Cyprus.
Bibliography: Bruce N.Kaye, “Acts’ Portrayal of Silas,” Novum testamentum, 21 (1979): 13-26.