But the natural knowledge of God is always a "cognitio legalis", a law knowledge.
[Luther:] They [the heathen Romans] know better how to govern external things than St. Paul and other saints Therefore the Romans also had glorious laws and statutes. For reason told them that murderers should be punished, that thieves should be hanged, and how inheritances should be distributed. All this they knew and did in a splendid and orderly way without any counsel or instruction fro the Holy Scriptures or the apostles... Although it was godless kingdom and persecuted the Christians bitterly, yet they ruled by reason and were respected by everyone. They kept the peace. At their time there was peace, and the world was open. This was an earthly, rational government.
Cato and Aesop and Cicero, and even the hated Aristotle, are better teachers of morals than their scholastic theologians. Of the pagan philosophers he said, "As far as their moral precepts are concerned, one can find no fault with the industry and the diligence of the heathen".
He recognized that from a sociological and political point of view the works and attitudes of the heathen might be called good. But from a theological point of view a man without the Holy Spirit is wicked, even if he is adorned with all virtue. Against the argument that reason is able to effect the most beautiful virtues and therefore cannot be under the devil, Luther says that the devil rules even in the best of our virtues. All the most admirable and most useful things in the world are damned by God.
Moreover, this knowledge of the law, excellent as it may be in itself, often leads men to pride and presumption. Coupled inextricably with this knowledge of the law is a legalistic concept of salvation. man naturally believes that he will be saved by "being good." A modern "philosophical defense of the Trinitarian-theistic faith" defends the righteousness of God by saying, "God's nature, then, is one which expresses itself in making the kind of world where some men go to heaven for obedience and some go to hell for disobedience." It is precisely this sort of theology that Luther rejects. "What good does it do you," he asks, "if all you can say is that God is gracious to the pious and punishes the wicked?"
[Luther] This pernicious opinion about the law, that it justifies, sticks very tenaciously to reason, and by it the whole human race is held so securely that it can be freed from it only with difficulty.
Human reason insists on making a tradesman out of God and says, "If I obey him, I will be in favor." In proud presumption reason seeks to strike a bargain with God and says, "if you will give, I will give." In this opinion both monk and Mohammedan agree. Both of them think that if I do this or that work, God will be merciful to me; if I do not, he will e angry.
... Man cannot free himself from such a quid pro quo (this in exchange for that).
... Speaking of his own life in the monastery, Luther said, "The holier we were, the blinder we became and the more purely we worshiped the devil." The heathen were guilty of a similar sin.
From there we get further exploration of the familiar themes of falling either into pride or despair. Even the heathen falls into despair in the light of this law.
This section brings back to me vaguely other very strongly worded statements about the unholy alliance between reason and works-righteousness. This is why, and which context, "reason" is the "whore". It can only give you the law and will make you "naturally" trust in the law. Reason cannot give you undeserved mercy in Christ, a gracious God. The "quid pro quo" trading system is not the same as the blessed exchange of my sins for his purity. It wants to trade my merits for a little bit of heaven.
This does not work because it robs God of his being God and gracious. It offends right against the first commandment.
God's word is enough and the thing needful.