The speculative learning of the theologians is altogether worthless. I have read Bonaventure on this, and he almost drove me mad because I desired to experience the union of God with my soul (about which he babbbles) through a union of intellect and will. Such theologians are nothing but fanatics. This is the true speculative theology (and it’s practical too): Believe in Christ and do what you ought.

Martin Luther, Tabletalk