The distinction between Erasmus and Luther was quite clear by the time the debate had settled into their contention over free will and election. Luther was always moving further toward assertive theology, toward proclamation. Erasmus, on the other hand, went hunting for an abstract scheme of salvation that would provide him with a little bit of grace, free will, and time to pursue righteousness.
Unlike Erasmus, Luther was not only interested in what “Scripture says but how Scripture functions in the argument over free choice.” How Scripture functioned to clarify itself was finally a matter of conscience. Luther wanted to know how the Word of God got preached in such a way that something was done to comfort and settle terrified consciences. Luther sought to express the clarity of Scripture by naming what the Word of God did to hearers. That is:
To put it briefly, there are two kinds of clarity in Scripture, just as there are also two kinds of obscurity: 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 perceives one iota of what is in Scriptures unless he has the Spirit of God. All men have a darkened heart, so that even if they can recite everything in Scripture, and know how to quote it, yet they apprehend and truly understand nothing of it. They neither believe in God, nor that they themselves are creatures of God, nor anything else...
For the Spirit is required for the understanding of Scripture, both as a whole and in any part of it. 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 Scriptures has been brought out by the Word into the most definite light, and published to all the world.
Working in this way Luther concluded that Erasmus’ words were, “Christ-less, Spirit-less words chillier than very ice.” (J.I. Packer, The Bondage of the Will, 75). Luther moved to preaching, where a preached, revealed and worshiped God is distinguished from the one who is hidden and wills to be unknown to sinners. For Luther, “it is not the task of theology to construct a theory of God that is supposed to win us over by attractiveness. It is the business of theology to foster the preaching of the Word of God” (Gerhard Forde, The Captivation of the Will: Luther vs. Erasmus on Freedom and Bondage, 27).
Luther moved to express the God who was crucified and hidden in Christ. Luther worked backwards from the hiddenness of God at the cross of Christ in order to understand how the Word of God was preached pro nobis, or for us. For, “God confronts us first of all in his word.”
The preached God does not in fact will the sinner’s death, as Ezekiel wrote in Ezekial 18:23.
However, the hidden God is lively, dangerous and unpredictable, imposing “death on us all and laid the Cross of Christ together with countless sufferings and afflictions on His beloved children and Christians” (LW 21:301).
In his formulation of how God wills to be known, it was impossible for Luther to agree with Erasmus’ conclusions because Erasmus persisted in his argument that the first concern of God's Word is morality rather than the larger issues of faith, reverence before God, and the deeper dimensions of the Christian life under the cross. For Luther, Erasmus’ Christ-less, Spirit-less theological conclusions demonstrated that behind his supposed humanistic optimism lay a profound despair and pessimism.
Although he attributed most things to grace, Erasmus argued that, “at the beginning and end of the process of salvation stood God’s action, but in between human beings also contributed something.” (Walter von Loewenich, Martin Luther: The Man and His Work, 268). At this point Erasmus liked to explain free will in this way,
...a child that is not yet able to walk falls. The father sets it on its feet again. Close by sits an apple. The child wishes to have it. It cannot reach the apple alone. But by taking the hand of the father it succeeds, and so it receives the apple as a ‘reward.’ The father could have carried the child, but the child could have struggled against being carried. For Erasmus, this was illustrative of ‘the cooperation between God’s grace and the human will’ (von Walter in “Queelenschriften zur Geschicthe des Protestantimus,” no. 8 cited in Lowenich, Martin Luther, 268-69).
True religion, or a philosophy of Christ, as Erasmus referred to it, had to be rational as well as moral. For Luther, this way of doing theology blasphemed God and uttered complete nonsense about creatures.
“This is what we come to when we seek to measure God and make excuses for Him by human reason, not reverencing the secrets of His majesty, but peering and probing into them; with the result that we are overwhelmed by the glory of them and instead of a single excuse we vomit a thousand blasphemies! We forget ourselves, and gabble like lunatics, speaking against both God and ourselves, while all the time we were intending, in the greatness of our wisdom, to plead both God’s cause and our own!” (Packer, Bondage of the Will, 200).
There was simply no neutral ground for Luther on which sinners could take a stand. One was either captive to God or the god of this world. Luther explained that, “the human will is placed between the two like a beast of burden. If God rides it, it wills and goes where God will... If Satan rides it, it wills and goes where Satan wills; nor can it choose to run to either of the two riders or to seek him out, but the riders themselves contend for the possession and control of it.” (Gordon Rupp, Luther and Erasmus, 140).
Erasmus wanted to make the power of the free will very slight and ineffective apart from the grace of God but, Luther asked, what can that little power do by itself?