And that’s not all. This third Person of the Godhead stands face to face and absolutely coequal in every way with the other two members of the Godhead, the great Jehovah and the mighty Logos (Jesus). But upon your regeneration as a child of God, the Holy Spirit actually consented to take up residence within your spirit and to offer His services to you! And one of the main reasons He came was to pray for you. Why did God send the Holy Spirit to live inside of you? So He could change you into the image of His Son. And in order to accomplish that goal, the Holy Spirit brought His own prayer language with Him so He could pray for all that concerns you.
From the book "The Hidden Power Of Speaking In Tongues"