(Cont'd from ch. 2)
4. How God knows - Here Luther applies himself to the question, "Does God foresee things contingently?" that is, Does God choose to save people because He foresees them saying "yes"? Or, Does God know, foresee things only according to His will? Luther answers yes to the second question: ...God foreknows nothing contingently, but that He foresees, purposes, and does all things according to His own immutable, eternal and infallible will. Luther acknowledges that this sentence is his "bombshell," that which will separate his readers into supporters or dissenters. He promises to support this Scripturally later; here he gives an argument based on the immutability of God, which Erasmus has to support (if he believes God to be kind, God must be unchangeably kind). If God is unchangeable, His will and wisdom are unchangeable, ultimately unaffected by the actions and choices of His creation. To put it differently, God's will cannot be contingent upon man, for it is God's will that brought man about in the first place.
5. Knowing how God knows matters - Why is this discussion important? If God knows things contingently, subjecting His will to the actions of creation, how can we believe His promises? Conversely, if God knows things unchangeably and necessarily (that is, powerfully causing them by His will), the believer has rock-solid confidence in those promises. ...the Christian's chief and only comfort in every adversity lies in knowing that God does not lie, but brings all things to pass immutably, and that His will cannot be resisted, altered or impeded. Luther then addresses Erasmus more directly, trying to show him the danger of his "cautious, peace-loving theology." Erasmus' seeking to turn people away from considering God's foreknowledge kept them, in Luther's opinion, from the very fountain of hope the Scriptures have for Christians.
Note: both Luther and Erasmus speak often of the "Sophists." As far as I understand, this is a general category included both the formal Sophists (a two-millenia-old Greek school of philosophy) and those given to philosophical speculation rather than Biblical study. I'd be happy to be corrected on my historical understanding here.
6. Why we can't suppress truth - Another of Erasmus' arguments was that, even if these things (predestination) were true, it would be impudent to expose them to everyone's hearing. Luther's reply is lengthy but simply summarized - what may be found in or proved by the sacred writings is both plain and wholesome, and so may safely be published, learned and known - and, indeed, should be. Erasmus truly desired peace in the Christian world and strongly believed that this discussion would never get us there; while he may have a point here, man's type of peace is not the highest goal of theology. The peace of God's gospel-truth is the highest goal. The price of the peace that Erasmus desires would be the souls of men, since they are denied the truth that sets free.
Erasmus used 1 Cor. 6:12 (all things are lawful, but not necessary); Luther counters first by showing that Paul was speaking not of doctrinal truth, but of application. Then Luther progresses to show other Scripture (2 Tim. 2:9, Mk. 16:15) commanding that the Word of God be proclaimed worldwide. Erasmus went so far as to assert that errors of church fathers and councils shouldn't be announced, lest the church be doubted. The whole point here, though, is that suppressing truth is tantamount to supporting untruth, which in turn is tantamount to imprisoning men's souls to untruth.