Using "pure speech" was one of the Restoration Movement's primary principles back in the "good old days." We popularized it using various mottos, most of which are long out of style. For example: "Using Bible Words for Bible Things" or "Bible Names for Bible Things." The idea was that using theological or denominational terminology only perpetuated division and sectarianism.
Today, however, language itself has come under fire. Postmodern philosophers maintain that words only mean what we want them to mean. Each individual, we are told, sees things differently and uses words to describe what they see or understand. Since no one can have absolute knowledge of anything, words are only relative to the understanding of the individual. Of course, we use words to describe the words that are only relative thus adding another layer to the mess! If words can't accurately express ideas, then we are left "up the creek without a paddle" and genuine communication is impossible.
I think it is amazing that God chose to communicate with us using words. He said that "in the beginnng was the Word." We understand that means Jesus for the Apostle John tells us a bit later in John 1 that "the word became flesh and dwelt among us." Nonetheless, God did communicate often (not always) through words. Evidently He is a good communicator because those who heard Him understood Him.
Since God could and did use language to communicate with us, it seems to me that I can trust what he says. Perhaps he picked the right words as he spoke. I think it is interesting that God's written Word was given to us in ancient Hebrew and koine Greek, two dead languages. The word meanings in those languages do not change. Our expression of those languages into English may shift a bit as we speak and write in a "living language" and living languages change. If you don't think so, explain what "swell" means or define a "besom" for me.
When we use terminology foreign to Scripture we add concepts to the Word of God never intended for communication. I might agree with Luther that the book of Romans teaches "justification by faith alone" but saying that conveys a meaning different from what Luther intended. Faith saves you, but as Jack Cottrell explains it saves you at baptism! It wasn't Luther or Calvin who corrupted the biblical language regarding the "link" between faith and baptism, it was Ulrich Zwingli.
Why are so many today hesitant to use the plain biblical language found in Acts 2:38? I was watching an old TV mini-series, "Anno Domini", the other day and even the script writers got Peter's Acts 2 speech right at the 38th verse! (Of course they later showed him baptizing someone by pouring water over his head. I guess they tried to keep everyone happy!) What is so hard about "speaking as the Scripture speaks?"
Our people avoided systematizing theology for a long time without harmful results primarily because they let the Word speak for itself. That's not to say that they didn't use inductive reason to discover doctrinal truth, they did! I think systematic theology is helpful when done accurately. I'd recommend The Faith Once For All" by Jack Cottrell as the best. But you know what? If more Christians would just read the Bible and believe what it says it would solve a lot of our problems.