Those who speak in strange tongues do not speak to others but to God, because no one understands them. They are speaking secret truths by the power of the Spirit.

What should I do, then? I will pray with my spirit, but I will pray also with my mind; I will sing with my spirit, but I will sing also with my mind.

When you give thanks to God in spirit only, how can ordinary people taking part in the meeting say "Amen" to your prayer of thanksgiving? They have no way of knowing what you are saying.

But in church worship I would rather speak five words that can be understood, in order to teach others, than speak thousands of words in strange tongues.