1 Corinthians 14:13

Wherefore let him that speaketh in an unknown tongue pray that he may interpret.

All religious services are to be conducted to edify others and to work for the perfection of the church. One who speaks in an unknown tongue is to pray for the ability to interpret it, so that the words can be understood and the church edified. The reason is that praying in an unknown tongue leaves the understanding unfruitful even while the spirit prays, whereas prayer is to be with the spirit and with the understanding also.

Worship must be intelligible so that the unlearned listener can understand what is said and join in saying Amen to blessing and thanksgiving, for thanksgiving may be good in itself yet fail in its purpose if the other person is not edified. In the church, speaking five words with the understanding in order to teach others is better than ten thousand words in an unknown tongue. The principle governing tongues applies equally to public prayer, testimony, and the use of the voice in the social meeting: speech must be clear and understandable, because words others cannot understand do not edify them.

The voice is a gift to be consecrated to God and cultivated so that the church is edified by what is said, and the habit of speaking in a low, indistinct way is a defect to be earnestly overcome, so that God is honored and His children are edified. A defect of voice does not excuse ceasing to offer public prayer or to bear witness to the power and love of Christ.