On October 31, 1517 an obscure university professor posted a list of 95 theses, or propositions, that he wished to debate. If you read them today they don't seem all that remarkable, and one could be forgiven for wondering what all the fuss was about. However, in the spring of the following year Luther published another set of 28 theses which came to be known as The Heidelberg Disputation. Luther was still a loyal Roman Catholic when he wrote these, but here you can see the seeds of the theology that would turn him from Martin Luther, Augustinian monk into Martin Luther, Protestant Reformer.
I especially love the last four:
25. He is not righteous who does much, but he who, without work, believes much in Christ.
26. The law says, "do this", and it is never done. Grace says, "believe in this", and everything is already done.
27. Actually one should call the work of Christ an acting work (operans) and our work an accomplished work (operatum), and thus an accomplished work pleasing to God by the grace of the acting work.
28. The love of God does not find, but creates, that which is pleasing to it. The love of man comes into being through that which is pleasing to it.
There in a few brief lines is summed up a theology of free grace alone (sola gratia) for which I give thanks on this Reformation Sunday.