1 Cor. 14:15 What am I to do? I will pray with my spirit, but I will pray with my mind also; I will sing praise with my spirit, but I will sing with my mind also.
Paul implied in one passage that, sometimes, the prayer language could actually be the language of angels. It is definitely “other worldly” and carries the sense of heaven and the presence of the Lord within it. In my early days as a Christian I was part of a Jesus community in California. In our services we would often sing and harmonize spontaneously and corporately in our heavenly language for extended periods of time. The Lord would manifest Himself in amazing ways as we pressed in together, singing in the Spirit. Those meetings were as close to heaven as one can get on this side. I also remember being in the Rodney Howard Browne service in Lakeland in January 1995 when the angels sang. It took place after an extended period of time of singing in the Spirit with several thousand believers. There is nothing comparable to those moments when heaven invades earth, it is beyond description. Here is a testimony about the heavenly gift from an Azusa Street Revival participant, Frank Bartleman.
“I was fully yielded to God, and simply carried by His will, as on a divine stream. I could have hindered the expression but would not have done so for worlds. A Heaven of conscious bliss accompanied it. It is impossible to describe the experience accurately. It must be experienced to be appreciated. There was no effort made to speak on my part, and not the least possible struggle. The experience was most sacred, the Holy Spirit playing on my vocal cords, as on an Aeolian harp. The whole utterance was a complete surprise to me. I had never really been solicitous to speak in “tongues.” Because I could not understand it with my natural mind I had rather feared it. I had no desire at the time to even know what I was saying. It seemed a soul expression purely, outside the realm of the natural mind or understanding. I was truly “sealed in the forehead,” ceasing from the works of my own natural mind fully.”
So don’t be afraid of the unexplainable things of God. There are definitely things we can never fully understand in this life, the power and fullness of His presence is one of those things.