One of the hazards that confronts fans of Martin Luther is translating his thought from the 1500's to the 21st century. Obviously Luther knew nothing of electric lights, computers, automobiles, airplanes, toasters, bicycles, steam engines, or iPhones. But technological advances are not the biggest problem.
Luther knew about the discovery of the Americas, just barely. But geography isn't the biggest challenge.
No, the biggest hurdle when we start to read Luther in 2014 is that he lived in the midst of "Christendom" -- that system in which the teachings and structures of the Christian church have huge power and influence over all areas of society. Luther assumes so many things because the Church in his day simply had power over the daily lives of people. So much of his thought is structured around Christendom, especially when it comes to solving practical problems.
So we always have to be cautious when we start taking his words and importing them wholesale into our own context, where the church's influence has waned, where we live within a multiplicity of world views, where the Bible is an important book, but not automatically considered authoritative.
Yet some of the time, Martin recognized that the power structures in his culture were not in fact living under the authority of the Church or acting out the teachings of the Bible. At those times he began to speak to our current situation a little more clearly. It is certainly possible to translate Luther's thought for a post-Christendom world, and I think it's hugely valuable to do so.
The other way of coming at Luther's teachings in this way is to find people who have been followers of Luther's version of Christianity who have themselves lived in post-Christendom contexts. That is one of the strongest arguments, in my mind, for paying close attention to a man like Dietrich Bonhoeffer, who followed Jesus in a Lutheran kind of way in the context of Nazi Germany, which maintained the facade of Christendom while denying its authority.