What is "Speaking in Tongues"

Speaking in tongues, as described in the Bible, refers to a phenomenon where individuals speak in languages they have not learned, often as a manifestation of the Holy Spirit. Here are some key points from the Biblical perspective:

Acts 2:1-4 - On the day of Pentecost, the Holy Spirit descended upon the apostles, and they began to speak in other tongues. This event is often cited as the origin of speaking in tongues in Christian tradition. The tongues were understood by people from various nations present in Jerusalem, each hearing the message in their own language.
1 Corinthians 12-14 - The Apostle Paul discusses spiritual gifts, including speaking in tongues, in these chapters. He distinguishes between:
Glossolalia - Speaking in tongues as a private prayer language where the speaker might not understand what they are saying but is speaking mysteries to God (1 Corinthians 14:2).
Xenoglossy - Speaking in tongues where the speaker utters recognizable human languages unknown to them, as in Acts 2.

Paul emphasizes that while speaking in tongues is a gift, it should be used in church settings with interpretation to edify the congregation, or else it might cause confusion.
According to 1 Corinthians 14, if someone speaks in a tongue in a church setting, there should be someone to interpret, so that the church may be edified. If there is no interpreter, the speaker should keep silent in the church and speak to themselves and to God.
In the context of the early church, speaking in tongues was seen as:
A sign for unbelievers (1 Corinthians 14:22).
A means of personal edification when there's no interpretation in public (1 Corinthians 14:4).
One of many gifts of the Spirit, not superior to others but to be desired alongside prophecy, which Paul esteems higher for its clarity in edifying the church.
There's a theological debate within Christianity about whether the gift of tongues has ceased (Cessationism) or continues (Continuationism). Cessationists argue that certain sign gifts, like tongues, were for the foundational period of the church to authenticate the message and messengers. Continuationists believe these gifts continue today.

In summary, speaking in tongues in the Bible is portrayed both as a miraculous sign for spreading the gospel across language barriers and as a spiritual gift for personal prayer and worship, which, if used in communal settings, requires interpretation for the benefit of all present.