How did the Jewish believers know that the Holy Spirit had been given to the Gentiles in Acts 10?
In Acts 10, the Jewish believers with Peter knew because they heard the Gentiles speak with tongues—other languages—and magnify God. That audible manifestation astonished them, demonstrating that the Holy Spirit had been poured out on Gentiles, something they had never witnessed before.
Les explains that the Jewish believers who came with Peter were astonished because the Holy Spirit was poured out on Gentiles (s546-s551). The way they knew was by an outward, audible sign: “they heard them speak with tongues or other languages and magnify God” (s554-s558). Les says this stopped Peter’s preaching in its tracks (s559-s560). Peter then asked, “Can any man forbid water, that these should not be baptized who have received the Holy Spirit as well as we?” and commanded them to be baptized in the name of the Lord (s561-s566). Les also notes that this reversed the order seen in Acts 2:38, where repentance, baptism, and remission of sins came before the gift of the Holy Spirit; here the Gentiles received the Holy Spirit first (s567-s584).
For they heard them speak with tongues, and magnify God. Then answered Peter,
More Questions
What did the Gentiles' speaking in tongues and magnifying God prove to the Jewish believers?
Hearing the Gentiles speak with tongues and magnify God proved to the Jewish believers that God was doing something they had not thought possible: saving a Gentile without making him a proselyte.