There is some truth in that idea. But only some. Jargon is part of what makes a group a group. If there is no distinction between inside and outside then there really is no group at all. History is filled with groups that have blurred, then blended, then blended into and then disappeared completely into the broader culture. It may take a few generations, but the end result is inevitable. Of course, once fully blended into the broader culture, then memory that there ever was such a group is forgotten, along with the lessons its demise might have given.
It is also simply not true that archaic jargon shuts a distinct group off from a steady influx of newcomers. In fact, it is not just a little untrue. It is patently and obviously untrue. We could mention Islam, with its ritual set of prayers and ceremonial motions and frequent use of ancient Arabic. We could mention the Latter Day Saints, with their seemingly odd customs and secret temple ceremonies. We could mention West Point, with their early nineteenth century clothing and carefully preserved phrases and traditions. None of these groups is lacking in newcomers or people waiting in line to become newcomers.
In 1990, when President Bush 1 visited a hospital ward of soldiers who had been wounded in Panama, he began his meeting with them by speaking to them in Latin: Semper fi. (short for semper fidelis, always faithful). He had been a Marine in World War II. He stepped into a room full of wounded marines. And, with two words, the President of the United States identified himself not simply as commander-in-chief, but as an insider. A fellow Marine. Two ancient words in a dead language that served as a clear boundary marker between insiders and outsiders.
When Paul is winding down his thoughts to the chaotic and divided church at Corinth, he interrupts his closing thoughts to say to them two words ordinary people on the streets of Corinth would have never understood. Marana Tha. The phrase is not Greek. It is Aramaic. מרנא תא O Lord, Come (or, possibly, the Lord has come). It was doubtless rooted in the earliest years of the church, when all its members were Jews and most spoke Aramaic. It must have come to Corinth as part and parcel of the jargon of this new community of (mostly) Greeks who believed not only in the monotheism of the Jews, but in the Messiah Jesus of Nazareth. Around forty or fifty years later, the writer of the Didache (ch. 10) will still use the same Aramaic words spelled out in the Greek alphabet: μαρὰν ἀθά.
Memorized passages spoken aloud. Ancient words not widely understood. Even gestures and rituals can all serve to strengthen the ability of communities to exist and continue within a broader and often foreign culture. We are surrounded by the inescapable evidence that this is true. But, if we are so blinded by the immediate as to weigh what we do and say in worship based solely on the absurdly short-sided concern for next week or even next year, then we can use, "Well, it worked for awhile" as a fitting epitaph.