1 Corinthians 14:14

'For if I pray in a tongue, my spirit prays, but my understanding is unfruitful.'

For praying in a tongue does not benefit the church at all. Indeed, says Paul, it is not only the church which does not understand me when I pray in tongues, I also do not understand myself. My mind is not involved. Praying in tongues may be of spiritual benefit because my spirit comes in close contact with God, Who does understand, but it does not benefit or assist my mind or my understanding. Nor does it benefit others.