For this reason the one who speaks in a tongue should pray that they may interpret what they say. 14 For if I pray in a tongue, my spirit prays, but my mind is unfruitful. 15 So what shall I do? I will pray with my spirit, but I will also pray with my understanding; I will sing with my spirit, but I will also sing with my understanding. (I Corinthians 14:13-15 NIV)
In the verse above Paul continues to emphasize the importance of understanding and knowledge in worship. Emotion in worship is good, but it must be guided by truth and knowledge. Paul is specifically discussion the case of the person who has the gift to pray to God in a supernatural tongue. Such a person should pray to God requesting that they may interpret what they say. After all, words spoken in a supernatural tongue are most certainly not meaningless. Meaning is very important, which is why Paul says if I pray in a tongue my spirit prays, but my mind is unfruitful. Paul says that we should not be content with an unfruitful mind. He tells us to both pray with our spirit, but also pray with our understanding.