It was on this date in 1517 that Martin Luther nailed his "95 Theses" on the church door at Wittenberg, thus beginning the theological and cultural movement that would be known as the Protestant Reformation.
For my Catholic friends who would like to read a quick, cogent description of what exactly were the foundations of the Reformation (which will also help you to understand the current convictions of your evangelical pals…like me), I think you'll find this an excellent piece.
Indeed, I'd suggest a careful reading of the article by evangelicals themselves who are known to sometimes get these very important matters kinda' muddled.
The article is from a Presbyterian pastor up in Michigan, Kevin DeYoung, and was passed on to me by another Presbyterian pastor for which I have great respect and affection, Dr. Phil Kayser from right here in Omaha.