Luther on The Limits of Human Reason

"Thus it is shown than human reason, the more it presumes to explore and fathom God's essence, works, and ways, goes farther and farther astray and finally comes to consider God as nothing and to believe nothing at all. Today there are more and more of such people who consider themselves great and wise. So it must go with all those who proceed apart from the bare Word and instead consult with reason about the articles of faith to see how they square with it. This is what has happened to those erring spirits of ours with regard to the Sacrament, Baptism, and other articles." LW 69:31-32