There are two aspects in the manifestation of tongues: first, the sign of tongues in Acts 2, 10, 19 (and probably in ch. 8); second, the gift of tongues in the early apostolic church. The gift under the second aspect evidently was not permanent (1 Cor. 13:9-13), nor given to every believer. It required the concomitant gift of interpretation (1 Cor. 12:10; 14:1-40). This sign gift with interpretation was meant to instruct the church before the completed NT Scriptures were given.
Under the first aspect tongues were a means by which the Holy Spirit witnessed to Israel on the day of Pentecost (2:4-13). They were a sign of the truth that Jesus was the Messiah and an indication of the new age of the Spirit.
The Jews were again challenged by the Samaritans receiving the Holy Spirit (Acts 8:14-17), and, although this is not specifically mentioned, they may have been given the evidence that the despised Samaritans had actually received the same gift as the Jews, by the sign of their supernatural utterances (cf. 11:17).
This is the use of tongues in the introduction of the gift of the Holy Spirit to Gentiles (Acts 10:44-47). Nothing could have been more convincing to skeptical, unbelieving Peter and his Jewish colleagues than the fact that Cornelius and the other Gentiles spoke in supernatural languages just as the Jews at Pentecost.
The disciples of John the Baptist who received the Holy Spirit and spoke in languages they had never learned (Acts 19:6-10) were a similar witness to the strong Jewish community at Ephesus. For the disciples of John the Baptist, whom the Jews generally accepted as a God-sent prophet, to be blessed by the Holy Spirit after being baptized in the name of the rejected Messiah, was of the deepest significance. But some of them [the Jews] became obstinate; they refused to believe as Isaiah (Is. 28:11-12) had predicted (1 Cor. 14:22).