In the Scriptures, therefore, no allegory, tropology, or anagogy is valid, unless the same truth is expressly stated historically elsewhere. Otherwise Scripture would become a mockery. But one must indeed take in an allegorical sense only what is elsewhere stated historically, as mountain in the sense of righteousness in Ps. 36:6: “Thy righteousness is like the mountains of God.” For that reason it is best to distinguish the spirit from the letter in the Sacred Scriptures, for this is what makes one a theologian indeed. And the church has this only from the Holy Spirit, not from human understanding. Thus Ps. 72:8 says: “May He have dominion from sea to sea.” Before the Spirits revelation no one could know that this dominion means a spiritual dominion, especially because he adds “from sea to sea” according to the historical sense. Therefore those who interpret this dominion as referring to the flesh and to earthly majesty have the killing letter, but others have the life-giving spirit.
Luther’s works, vol. 10: First Lectures I