To be brief, there are two kinds of clarity in Scripture ... : one external and pertaining to the ministry of the Word, the other located in the understanding of the heart. If you speak of the internal clarity, no man perceived one iota of what is in the Scriptures unless he has the Spirit of God ... If, on the other hand, you speak of the external clarity, nothing at all is left obscure or ambiguous, but everything there is in the Scripture has been brought out by the Word into the most definite light, and published to all the world.
— Martin Luther, On the Bondage of the Will, in Luther and Erasmus: Free Will and Salvation (ed. by E. Gordon Rupp and Philips S. Watson; Philadelphia: Westminster Press: 1969)