According to the Apostle Paul, in his first epistle to the Corinthian Church, every believer receives at least one of nine spiritual gifts (12:11). The nine are: Apostles, Prophets, Teachers, Workers of Miracles, Workers of Healings, Helpers, Governments (Leaders), Tongues, and the Interpreters of Tongues (12:28, 30). The gift of tongues, like all of the spiritual gifts, is given by the Holy Spirit to some of the members of the Body of Christ (12:4-30).
The purpose of the gift of tongues is as a sign to unbelievers: "Wherefore tongues are for a sign, not to them that believe, but to them that believe not" (14:22). And although it is not specifically stated as such, that would mean tongues were for witnessing to unbelieving Jews; "For the Jews require a sign, and the Greeks seek after wisdom" (1:22). The first instance where speaking in tongues is mentioned is on the Day of Pentecost in Acts 2:4-11:
"And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance. And there were dwelling at Jerusalem Jews, devout men, out of every nation under heaven. Now when this was noised abroad, the multitude came together, and were confounded, because that every man heard them speak in his own language. And they were all amazed and marvelled, saying one to another, Behold, are not all these which speak Galilaeans? And how hear we every man in our own tongue, wherein we were born? Parthians, and Medes, and Elamites, and the dwellers in Mesopotamia, and in Judaea, and Cappadocia, in Pontus, and Asia, Phrygia, and Pamphylia, in Egypt, and in the parts of Libya about Cyrene, and strangers of Rome, Jews and proselytes, Cretes and Arabians, we do hear them speak in our tongues the wonderful works of God."
Notice that those listening, Jews from all over the known world, heard the disciples speaking about "the wonderful works of God" in their native languages. These Jews responded with great interest in what the disciples had to say. As a result, 3000 were "added to the Church" (Acts 2:41). To be continued.