1 Corinthians 14:9
So likewise ye, except ye utter by the tongue words easy to be understood, how shall it be known what is spoken? for ye shall speak into the air. So likewise ye, except ye utter by the tongue words easy to be understood, how shall it be known what is spoken? for ye shall speak into the air.
Speech must be plain and easy to understand, for otherwise hearers cannot know what is spoken and the utterance is wasted as speaking into empty air. Lifeless instruments such as pipe or harp must give a distinction in sounds in order to be recognized, and the trumpet must give a certain sound to prepare for battle, so the tongue must utter meaning that can be understood. There are many voices in the world and none is without meaning, but without shared and known meaning speaker and hearer remain foreigners to each other, so those eager for spiritual gifts should seek to excel to the edifying of the church, with words clear in meaning so the church can be built up.
Unintelligible utterance offered as the gift of tongues is not a genuine gift from God but false, producing harmful excitement instead of spiritual growth. Indistinct delivery can destroy the force of a thought, while simple words spoken distinctly make it plain. The same principle applies to prayer and testimony in religious meetings, which should be clear and audible so others can understand, be taught, and be edified.
A low, indistinct voice is a defect to be overcome by cultivating and consecrating the voice to God, not a reason to stop speaking. Those who would work for God must learn to tell what they know convincingly and impressively, in a clear, straightforward, plain, distinct manner with expression and a controlled voice in full, round tones. This applies especially to ministers, evangelists, Bible workers, and canvassers preparing for service, and indeed to workers in any calling, because the more expression put into words of truth the more effective they are on hearers, proper presentation of truth is worthy of the highest effort, and without this training they are shorn of half their influence for good. In ministerial work more attention must be given to culture of the voice, for knowledge is of little advantage and education is of no avail unless ideas are clothed in appropriate language and the talent of speech is cultivated to use the voice correctly, so that without this the work fails, while knowledge combined with the ability to speak wise, helpful words in a way that commands attention is a wonderful power.