So the person who speaks in another language should pray for an interpretation of what he says.
If I pray in another language, my spirit prays, but my mind is not productive.
So what does this mean? It means that I will pray with my spirit, and I will pray with my mind. I will sing psalms with my spirit, and I will sing psalms with my mind.
Otherwise, if you praise God only with your spirit, how can outsiders say "Amen!" to your prayer of thanksgiving? They don't know what you're saying.
Your prayer of thanksgiving may be very good, but it doesn't help other people grow.
I thank God that I speak in other languages more than any of you.
Yet, in order to teach others in church, I would rather say five words that can be understood than ten thousand words in another language.
Brothers and sisters, don't think like children. When it comes to evil, be like babies, but think like mature people.
God's word says, "Through people who speak foreign languages and through the mouths of foreigners I will speak to these people, but even then they will not listen to me, says the Lord."
So the gift of speaking in other languages is a sign for unbelievers, not for believers. The gift of speaking what God had revealed is a sign for believers, not for unbelievers.
Suppose the whole congregation gathers in the same place and you speak in other languages. When outsiders or unbelievers come in, won't they say that you're out of your mind?