7 Even things without life, whether flute or harp, when they make a sound, unless they make a distinction in the sounds, how will it be known what is piped or played?
8 For if the trumpet makes an uncertain sound, who will prepare for battle?
9 So likewise you, unless you utter by the tongue words easy to understand, how will it be known what is spoken? For you will be speaking into the air.
10 There are, it may be, so many kinds of languages in the world, and none of them is without significance.
11 Therefore, if I do not know the meaning of the language, I shall be a foreigner to him who speaks, and he who speaks will be a foreigner to me.
uncertain (v.8) = indistinct, lacking in clearness
prepare for battle (v.8) — one trumpet sound called soldiers to battle, another called them to rest. If the trumpet couldn’t be understood, the soldier wouldn’t know what to do.
tongue (v.9) — here, referring to the physical tongue in comparison with instruments
into the air (v.9) — as though there were nobody to hear
it may be (v.10) — the exact number is immaterial
languages (v.10) — actual languages, known to those who speak them
foreigner (v.11) = barbarian — Used in Paul’s day of anyone who didn’t speak Greek
There are many, many languages, not one of which is unintelligible, for every language on earth is understood by those who speak it. But to a Greek, an address in a foreign language is of no value, and is not more than gibberish to him. This holds true in the Church. Unless there be an interpreter, he who speaks in an “unknown tongue does not know what he is saying, nor do those who listen: and the voice of language is useless. — Greene, page 448.
Two points:
These verses make it very clear that the gift of tongues referred to existing languages. Paul comes right out and says in verses 10 and 11 that he’s talking about languages that are understood by native speakers.
If the Bible said nothing else about tongues except what is in these five verses, they would be enough to show that tongues, as it is practiced today, is not of the Holy Spirit. Unintelligible gibberish conveys no meaning to the hearers, is of as much value as if there were no hearers, and makes the speaker a barbarian.