Are tongues a sign for believers or unbelievers? 1 Corinthians 14:22-25 confuses me. Verse 22 states:


  Tongues, then, are a sign, not for believers but for unbelievers; prophecy, however, is not for unbelievers but for believers.


So, tongues is a sign for unbelievers. But then, verses 22-25 go on:


  So if the whole church comes together and everyone speaks in tongues, and inquirers or unbelievers come in, will they not say that you are out of your mind? But if an unbeliever or an inquirer comes in while everyone is prophesying, they are convicted of sin and are brought under judgment by all, as the secrets of their hearts are laid bare. So they will fall down and worship God, exclaiming, “God is really among you!”


These two parts seem in contradiction. And this also applies (in reverse) to Paul's comments on prophecy.

Can anyone explain this?
The whole 14 chapter of 1 Corinthians is dedicated on how the Christian meeting must operate. It was good to talk in tongues in many cases but a problem may occured when "everyone speaks in tongues". Paul recommend an organized way for the operation of Christian meetings. He also recommended that the speaking in tongues “be limited to two or three at the most, and in turns.” However, if no one could translate, then the person speaking in a tongue was to remain silent in the congregation, speaking to himself and to God. (1 Corinthians 14:22-33)