If you speak to people in words they don’t understand, how will they know what you are saying? You might as well be talking into empty space. (1 Corinthians 14:9).
Paul originally wrote these words to those who were exalting the gift of tongues (speaking in a foreign or spiritual language you have been given supernaturally) in worship. His point was the church should exalt the gifts that reach others more than the gifts that simply enrich the individual.
As I read those words I see another application. We must also be wary of speaking "Christianese" to friends and neighbors. Words like, "saved," "righteous," "atone," "Rapture," "Judgement seat" and even "believe" (there are lots more), are words that most non -Christians don't understand. When we use our own jargon (even though they are all great words) our friends may give you a blank stare.
Here's the challenge: 1) We must watch our language. 2) We must know what these words mean. 3) "translate" these words and concepts into terms your friend or family member will understand. We must not water down the truth or the meaning of the words but we do need to accurately translate.
We are living in a rapidly changing post-Christian world. As any good missionary, we need to learn the language of the people to whom we speak and then find a way to communicate the truth of the gospel in words they will understand. It is a message they desperately need to hear and understand.