Speaking in tongues was the miraculous ability to speak in a foreign language or dialect, without any previous study or experience (Acts 2:1-11). Therefore, it is incorrect to claim that this was the ability to speak in an angelic or heavenly language. And neither was this gift used exclusively or even primarily for private prayers (1 Corinthians 14:14-16). Non-Christians could perfectly understand the tongue-speaker (Acts 2:11). This gift was not the proof that one was a genuine Christian. For all Christians didn't possess this gift (1 Corinthians 12:30) and some very unspiritual individuals did (1 Corinthians 3:1-3). This gift ceased, as did all the miraculous gifts when God's revelation (the New Testament) was complete (1 Corinthians 13:8-13).