Why does the Bible say speaking in an unknown tongue is to God and not to men?
An unknown tongue is directed to God because no man can understand it; it cannot be deciphered or reduced to print. Only God could make anything out of it if possible. The speaker, in his own spirit, speaks mysteries that men cannot comprehend, so the message is not to men.
Les explains that Paul is dealing with tongues, or languages, in the context of chapters 12 and 14. The unknown tongue is not understood by people: no man understandeth him, and no one can decipher it or reduce it to print. Paul says no one speaks in an unknown tongue to men but to God, because God is the only one who could make anything out of it if it were possible. In his own spirit—the man’s spirit, not the Holy Spirit—he speaketh mysteries. Les also connects this to pagan religions, where mysteries are at the core and only the inner sanctum comprehends them, while those on the fringe do not.