1 Cor 14:2.
God has given us a supernatural language. After becoming born again the Holy Spirit came to dwell in us. However there is a subsequent in filling of the Holy Spirit that we each have a right to as children of God. The initial evidence of this is speaking in tongues.
When you speak in tongues you are speaking to God in a language that no man understands. You are praying out mysteries, things that you don't know of.