Tongues is the Power to preach in a Tongue which is otherwise unknown to you.
For example, Turkish -- this Tongue is not natively known to me. If God gave it to me to preach the Gospel in Turkish for a season, I would have to totally trust the Spirit for utterance (just as Acts 2 says), for the Turkish tongue is unknown to me.
14 For if I pray in an unknown tongue, my spirit prayeth, but my understanding is unfruitful.
Continuing the thought, IF God gave it to me to preach the Gospel in Turkish, that is a great and miraculous thing... but why on earth would I use the Gift to pray in Turkish? That would be an Unfruitful use of the Gift; it profits me nothing to pray in a gifted Foreign Tongue, which is granted for a season and for an intended and specific purpose (when it is granted at all).
15 What is it then? I will pray with the spirit, and I will pray with the understanding also: I will sing with the spirit, and I will sing with the understanding also.
Instead, you should pray in the Tongue which is native to you. That is Fruitful.
16 Else when thou shalt bless with the spirit, how shall he that occupieth the room of the unlearned say Amen at thy giving of thanks, seeing he understandeth not what thou sayest? 17 For thou verily givest thanks well, but the other is not edified.
Because by praying in the gifted Tongue of Turkish, I have denied my fellow English-speaking brethren the opportunity to signify, "Amen"!! If gifted the Tongue of Turkish, let me preach the Gospel to Turks; but it is not a Gift for Prayer.
18 I thank my God, I speak with tongues more than ye all:
Of course. Paul was sent all over the Gentile World.
19 Yet in the church I had rather speak five words with my understanding, that by my voice I might teach others also, than ten thousand words in an unknown tongue.
But in home churches, he considers it best only to speak in the home tongue. The fact that God has given him to speak Libyan and Cyrene and Latin (or whatever) might look kinda nifty-cool to the Ephesian Church, but it would not edify their understanding (they would not understand his words... almost as bad as babbling gibberish!!).
I submit that my analysis above is precisely commensurate with the explicit wording of the Text, and the explicit normative example from Acts that Tongues is a Gifted Power over Foreign Language.
I submit further that you will reject it, for it overthrows your position entirely; and your Gospel of Gibber is more precious to you than the actual words of Scripture.
Where your treasure is, there will your heart be also.
For if I pray in an unknown tongue, my spirit prayeth, but my understanding is unfruitful.