For the first few years of the church's existence, only Jews believed in Jesus as their Savior. But Jesus had promised that His message would go out to all the world.

But you shall receive power when the Holy Spirit has come upon you; and you shall be witnesses to Me in Jerusalem, and in all Judea and Samaria, and to the end of the earth (Act 1:8).

In Act 10, the Gentiles (non-Jews) received the Holy Spirit. The first Gentile believers were Cornelius and his family. When the word was preached to them by Simon Peter, a personal disciple of Jesus Christ and a leader of the church, they believed the message.

While Peter was still speaking these words, the Holy Spirit fell upon all those who heard the word. And those of the circumcision who believed were astonished, as many as came with Peter, because the gift of the Holy Spirit had been poured out on the Gentiles also. For they heard them speak with tongues and magnify God. Then Peter answered, Can anyone forbid water, that these should not be baptized who have received the Holy Spirit just as we have (Act 10:44-47).

There are those who point to this passage as another indication of the gift of tongues as the sign of receiving the Holy Spirit. But this is not the case. In this instance, the tongue-speaking of the Gentiles convinced Peter and the other Jews that Gentiles were now part of the Christian church. Because the Gentiles exhibited the same supernatural ability to speak in tongues as the Jews did on the Day of Pentecost, it was clear that they too had received the Holy Spirit.

When Peter later recounted the story, the Jews rejoiced.

When they heard these things, they became silent; and they glorified God saying, Then God has also granted to the Gentiles repentance to life (Act 11:18).

The sign of tongues in this case, then, was to believing Jews to show them that God also had granted forgiveness of sins to Gentiles as well as to Jews.