1 Corinthians 14:19-22

19 However in the assembly I would rather speak five words with my understanding, that I might instruct others also, than ten thousand words in another language.

20 Brothers, don't be children in thoughts, yet in malice be babies, but in thoughts be mature.  21 In the law it is written, "By men of strange languages and by the lips of strangers I will speak to this people. Not even thus will they hear me, says the Lord."  22 Therefore other languages are for a sign, not to those who believe, but to the unbelieving; but prophesying is for a sign, not to the unbelieving, but to those who believe.