Speaking in tongues is a gift from the holy spirit which started in the new testament. Speaking in tongues started on the day of Pentecost when all the disciples gathered in one room and were praying, the holy spirit came down and they began to speak in different languages. That day the disciples speak in language which no one understood but only by God. Speaking in tongues is a powerful language that can cast away demons.
The bible also teaches us that speaking in tongues can be a personal language which a believer can use to communicate with God. When a Christian speaks in tongues, it strengthens his spirit. Only those who are in spirit can speak in tongues because when you're in spirit that's when the holy spirit comes down.
The bible also says that living a good life and doing the will of God is much more important than any spiritual gift. Speaking in tongues doesn't make us much more holy than others who don't speak.
