In Greek the word ἰδιώτης (idiotes) is used to refer to that which belongs to one’s own self. The English word idiom is a derivative. So is the word idiot, meaning someone who is uneducated or unskilled. This Greek word is used of a private person, that is, one who has not been formed by the greater wisdom of those who have understanding. There is not necessarily any sin in being unlearned in certain areas; certainly no one would call me for advice on how to throw a baseball or repair an aircraft. But it would be nothing short of fraudulent for me to don the coveralls of the aircraft mechanic and begin turning wrenches on a set of stuck landing gear. And even if, by some miracle of trial-and-error I were able to make the landing gear work again, my repair would almost certainly not withstand the rigorous testing that atmospheric flight puts on such structures. In short, as regards aircraft maintenance, I am an idiot. Any work I would do on an airframe would necessarily be idiotic, that is, it would be my own. It would not conform to any standards or known universal set of best practices.
In the world of powered flight, there is no room for idiotic (i.e., uneducated and self-made) repairs. In the Church, there is no room for idiotic theology. Both are forbidden and for the exact same reason. Theology must never be idiotic; it must never belong to a single person. It must never belong to a single time, or a single people, or a single issue. Theology is best when it is the least idiotic, when it is the most universal and thoughtful.
When we evaluate a theological statement, we should at least consider whether the statement is idiotic – whether it is actually created hastily by a single person to patch up some emergency or whether it is, in fact, what the catholic Church has always taught. Even good theological statements like those in the Confessions which were written in response to a specific issue of the time did not invent a new theology as the response, but rather confessed that which the Church has always taught. In fact, the Lutheran fathers took great care to produce the witness of those fathers that had come before them to prove that the Lutherans were teaching nothing new.
To avoid following idiotic theology, I can give no better advice than the command written by St. Paul: “Follow the pattern of the sound words that you have heard from me, in the faith and love that are in Christ Jesus” (2 Timothy 1:13). Good theology has certain patterns of words that are time-tested and get handed down from one generation to another: Law and Gospel, the incarnation of Jesus Christ, the righteousness of faith, salvation by grace alone through faith alone, and so forth. When a teacher in the church changes these comfortable, familiar patterns of sound words and boasts of some new set of words, one is right to be suspicious that the doctrine being promoted may well be idiotic.
Most importantly, the only way for you to be able to sort out the genuine article from idiotic imposters is to be formed yourself by those patterns of sound words. Read your Bible. Come to Church every week. Come to Bible class. Pray. Ask tough theological questions of your pastor. Ask your pastor to recommend a good theological book for you to read – he’ll know one that’s right for you. Hearing God’s Word, reading good theology, and fervent prayer – these things will not only help you to discern and guard against idiotic theology, but will bring you out of your own private idiom and into the theology of the Church catholic.