17 You might be giving thanks well enough. But the others are not being built up.
18 I thank God that I speak in other languages more than all of you do.
19 But in the church I would rather speak five words that people can understand than 10,000 words in another language. Then I would be teaching others.
20 Brothers and sisters, stop thinking like children. Be like babies as far as evil is concerned. But be grown up in your thinking.
21 In the Law it is written, "Through people who speak unfamiliar languages and through the lips of strangers I will speak to these people. But even then they will not listen to me." (Isaiah 28:11,12) That is what the Lord says.
22 So speaking in other languages is a sign for those who don't believe. It is not a sign for those who do believe. But prophecy is for believers. It is not for those who don't believe.
23 Suppose the whole church comes together and everyone speaks in other languages. And suppose visitors or unbelievers come in. Won't they say you are out of your minds?