The mind will be unfruitful; it is just a work of the spirit. The Apostle says: “For if I pray in a tongue, my spirit prays, but my understanding is unfruitful” (v.14). The Apostle could see that this state should be completed by understanding. The person should pray in spirit and also with understanding; sing in spirit and also with understanding. Although the Apostle mentions the phrase ‘edifies himself’ very cautiously and with remarks, and points out that it is not a complete edification, yet for the sake of edification he says: “I thank my God I speak with tongues more than you all; yet in the church I would rather speak five words with my understanding, that I may teach others also, than ten thousand words in a tongue” (vv.18, 19).