A Biblical Christian is not a progressive, because he believes in an unchanging Truth and source of truth: the God of Abraham, Isaac, and Jacob.
"Conservatives" believe that truth is unchanging, that we should search for truth, and once we've found it, hold on to it. Truth is unchanging, and external. History is extremely valuable because it shows a record of the search for truth, and we can learn from what others have found and rejected. The elderly are a great resource, because they have had so many more years to search for truth, and the truth they've found is as valuable to us today as when they first found it.
Biblical Christianity is rooted in history: just as the phrase "Abraham, Isaac, and Jacob" shows! Biblical Christians believe that truth is to be conserved, but they are more than just "conservative," just as they are more than just "evangelical." Biblical Christianity is a comprehensive worldview, which speaks to every area of life, which is something that mere political conservatism or theological evangelicalism does not. And of course the Biblical Christian goes even further then just relying on their own minds to recognize truth. We know that God has revealed Truth to us in Jesus, and that He gives us the Spirit to guide us into all truth!
I think some of the popular confusion over the terms "progressive" and "conservative" comes when conservatives are thought of as living in the past. The cariacture would be of a progressive driving a Mini Cooper while the conservative bounces around in an Amish buggy. But this is absurd. If you look at chemistry for a minute, I'll show you what I mean. Does each new chemist need to reinvent the Periodic Table? Does each chemist have his own version of the Periodic Table? No, and no, because the elements (or a number of them, anyway) have been discovered, and each of us lives in a world that shares the same elements. The universal truth here is that we share reality, and some descriptions of that reality are valid, and some are invalid. The elements have fixed characteristics, and understanding what others have discovered about the elements is the first step toward making your own new discoveries.
So let us be clear: in basic science, it's not the elements that are changing; it's our understanding of them. Reality is fixed. Our understanding and descriptions are changing. When you next hear that "in science, everything's always changing," bear this in mind.
The fun comes once you've discovered some truth, and then get to apply it to new situations. An example in chemistry is that you can take the "old" elements, and assemble them into new compounds. The conservative realizes that the elements aren't going to change (well, says the Biblical Christian, at least not until God brings the meltdown), and that's extremely comforting. You don't have to worry that a compound composed of carbon, hydrogen, and oxygen one day is going to be composed of silicon, helium, and sulfur the next! You don't have your set of elements that are completely different from your labmate's, so when you talk about compounds, you're talking about a shared reality. If you draw methane with one carbon and five hydrogens, your labmate doesn't sigh and say "Only in your world" (unless he's a wiseacre). He points out that you've made a mistake, and you thank him for it (unless you're a wilting violet). You have shared reality. Some descriptions are valid, and some are invalid. Thinking that you can invent your own box of molymods and make your own elements can be exhilirating -- until you discover your self-deception. You can start with past chemists' discoveries and analyses to get something of a handhold on the field, then plan your own work. New compounds can be formed, but the things that remain constant from creation to heatdeath are the foundation the rock you're climbing stands on. There's so many possible combinations of elements and methods to combine them that no one is in fear of exhausting the possibilities of new synthetic marvels. Thus, conservatism offers a link with the past, and a basis for hope for the future.
Conservatism offers a way to build on what others have discovered, instead of feeling the crushing burden of inventing your own reality. Beyond just the chemistry of life, once you have truth, you can begin to apply it -- that's the fun of it! You don't have to wander through life in the dark with your fingers groping forward, looking for your own person set of truth. You're not a golden-bellied god with enormous earlobes, sitting in the lotus position creating truth from scratch. You're a goldpanner, sifting the sands ot time with a worldview. You have a few thousand years' worth of material to filter, and you can look for the good stuff while striking out on uncharted territory to apply the truth you've discovered to old and new situations.
Given this situation, why would anyone believe in progressivism? There's something attractive in being one's one master, in feeling that everything is fluid, and that you can shape your own reality. Anyone who as a child thought that shutting one's eyes prevented anyone else from seeing them has experienced and probably enjoyed this delusion -- for a time. But convincing oneself of a falsehood does not make the falsehood true. I would say that there are idealists and opportunists who are progressives. The idealists truly believe, while the opportunists see how malleable a man is when he has no foundation. Think of the inheritance tax, and the anger many progressives feel toward a situation where a man can leave an inheritance to his children. In the same way, many progressives are angry at a situation where a man can teach what he sees as truth to his children. If the children were set loose in the world with no guide and no mentor, it would take them years to learn the truth that previous generations have discovered. They would probably never catch up. Without knowing any of the truth uncovered or revealed during history, these children foundationless -- and extremely gullible. And extremely manipulatable. For just as truth remains truth, unchanged by time, falsehood remains falsehood, unchanged by time. While truth can be rediscovered after being neglected for a time, falsehood can be rediscovered after being neglected for a time. There's a reason why a declared goal of Marxism-Leninism (the fountainhead of "progressivism" is to disconnect a people from its history. Truly, which false idea of today is really "new"? Free love? Abortion? Euthanasia? Socialism? Been there, done that. They were wrong when they were first introduced, and they are wrong now. "Progressivism" is truly "Regressivism," because it simply reawakens past falsehoods and tries to pass them off as novel. The idea of our own individual goddishness was wrong when Satan's forked tongue tickled Eve's ear with "You will be like God!" and it is still wrong today. How do those sayings go? "Those who stand for nothing fall for anything." Oh yeah, and "Those who do not study history are doomed to repeat it" which could also be stated as "Those who study history believing that nothing those fuddy-duddies called truth is still truth today are doomed to repeat it."
 Alexander Hamilton
 George Santayana