Speaking in tongues is the New Testament phenomena where a person speaks in a language that is unknown to him. This language is either the language of angels or other earthly languages (1 Cor. 13:1). It occurred in Acts 2 at Pentecost and also in the Corinthian church as is described in 1 Corinthians 14. This New Testament gift was given by the Holy Spirit to the Christian church and is for the purpose of the edification of the Body of Christ as well as for glorifying the Lord.
There seem to be three divisions in the use of tongues: First, a private prayer language that is not interpreted; second, a language that is interpreted -- this defines proper usage in the Christian congregation; and third, missionary context -- that is, it appears in the context of evangelism where people (in the New Testament) are presenting the gospel.
Today there is much debate as to the validity of speaking in tongues, especially since there is so much misuse of it in Christian circles. Nevertheless, some Christian churches teach that all the charismatic gifts (speaking in tongues, word of knowledge, prophecy, etc.) have ceased with the completion of the New Testament (1 Cor. 13:8-12). Others maintain that the charismatic gifts are still for the church today (1 Cor. 1:7). It is not the purpose of this paper to take sides on this issue since it is so divisive and believing or not believing in them does not affect one's salvation. Nevertheless, there are good arguments on both sides, and the Christian church needs to be as gracious as possible to those with opposing views on this debatable issue.
But there is an important point worth making here. Some churches erringly maintain that you must speak in tongues in order to be saved. This is a grave mistake since not all people speak in tongues because not all people are gifted by the Holy Spirit this way.
1 Cor. 12:7-11,28-31, "But to each one is given the manifestation of the Spirit for the common good. 8 For to one is given the word of wisdom through the Spirit, and to another the word of knowledge according to the same Spirit; 9 to another faith by the same Spirit, and to another gifts of healing by the one Spirit, 10 and to another the effecting of miracles, and to another prophecy, and to another the distinguishing of spirits, to another various kinds of tongues, and to another the interpretation of tongues. 11 But one and the same Spirit works all these things, distributing to each one individually just as He wills...28 And God has appointed in the church, first apostles, second prophets, third teachers, then miracles, then gifts of healings, helps, administrations, various kinds of tongues. 29 All are not apostles, are they? All are not prophets, are they? All are not teachers, are they? All are not workers of miracles, are they? 30 All do not have gifts of healings, do they? All do not speak with tongues, do they? All do not interpret, do they? 31 But earnestly desire the greater gifts."
So, the gifts of the Spirit are varied, and they are for the edification of the body of Christ. Speaking in tongues is not necessary for salvation, and it is not a prerequisite proof of Baptism in the Holy Spirit. We must remember the words of Paul in 1 Cor. 13:1-2,13
"If I speak with the tongues of men and of angels, but do not have love, I have become a noisy gong or a clanging cymbal. 2 And if I have the gift of prophecy, and know all mysteries and all knowledge; and if I have all faith, so as to remove mountains, but do not have love, I am nothing.... 13 But now abide faith, hope, love, these three; but the greatest of these is love."
Inside the Bible
Mark 16:17, “These signs will accompany those who have believed: in My name they will cast out demons, they will speak with new tongues."
In the New Testament
Acts 2:3–4, "And there appeared to them tongues as of fire distributing themselves, and they rested on each one of them. 4 And they were all filled with the Holy Spirit and began to speak with other tongues, as the Spirit was giving them utterance."
1 Corinthians 12:10, "and to another the effecting of miracles, and to another prophecy, and to another the distinguishing of spirits, to another various kinds of tongues, and to another the interpretation of tongues."
Is speaking in tongues a necessary sign of salvation?
No, speaking in tongues is not a necessary sign of salvation. We see in Acts that many people who became Christians immediately spoke in tongues (Acts 2:4; 10:46; 19:6). Not all speak in tongues because God doesn't give the gift to everyone. Speaking in tongues is not the sign of salvation but a sign. If anything, the fruit of the indwelling Spirit of God as listed in Gal. 5:22-23 is the sign of salvation.
"The description of a vision given to the disciples at the PENTECOST event (Acts 2:1–13). In view of the familiar biblical association of fiery apparitions with visions of God (e.g., Ezk. 1:27; Dnl. 7:9f.; see also FIRE I.D.), as well as passages such as 1 12En 14:8–15; 71:5, which refer to “tongues of fire” in the context of visions of heaven, the phenomenon in Acts likely symbolizes divine presence and activity, which is seen “distributed” upon the disciples (2:3; AV “cloven” is a mistranslation). The phrasing “as of fire” in this description of the inauguration of the Church bears some similarity to the same writer’s account of the beginning of Jesus’ ministry in Lk. 3:22; there Jesus sees the Spirit descending “in bodily form, as [hōs] a dove.” The author may have intended to draw a parallel between the two visions that accompany scenes of empowerment by the Spirit." (Bromiley, Geoffrey W., ed. The International Standard Bible Encyclopedia, Revised. Wm. B. Eerdmans, 1979–1988.)