On the free will they teach that the human will has some freedom toward effecting civil righteousness and choosing matters that are subject to reason. But it does not have the power, without the Holy Spirit, to effect God's righteousness, that is [seu] spiritual righteousness, since "the natural man does not perceive the things that belong to the Spirit of God." [1 Cor. 2.4] This, rather, comes about in hearts when the Holy Spirit is received through the Word. Augustine says as much in so many words (Hypognosticon, Book 3): "We confess that all men have a free choice (albeit that possesses the judgment of reason), not that it is thereby suited to begin or, certainly, complete in respect of those things that have to do with God, but only in respect of those works of the present life, both good and evil...."
The Wittenberg settlement between Christian teaching and Humanism (last post) honors this Scriptural assignation of powers to the free will. Humanism is one of those good works spoken of and belongs to left-hand realm of God, where the free will does have a choice. (Get ready for the next sentence; sorry it's a Teutonic doozy.) And just as choices in congregational life such as whether to build a new nave or not belong to the left-hand realm but impact for better or for worse the right-hand realm, where God rules through His Word and Sacrament, so too does the choice under the purview of human judgment and within the realm of the free will, the choice of Humanistic vs. scholastic learning, or, in short, the choice of the kind of learning that the Church wishes to support and pursue, have an impact for better or for worse on the right-hand realm, where the human task is rightly to understand, speak, confess, and proclaim God's Word. In Lutheran theology, that choice remains right where it belongs: in the realm of the left. That is, it does not, as with Zwingli and Erasmus, drive the theological agenda. However, it is not a value-less choice, but one undertaken only in the face of what can and does properly support the understanding and teaching of the Gospel--not just for clergy-to-be, but for all Christians.
Faced with precisely that choice, and informed by their theological agenda, the Wittenberg Reformers adopted Humanism, literae humaniores, the classics, along with the languages, as that vehicle that surpassed every other in aiding a solid understanding of (a) the realm of the left; and (b) the realm of the right. But it was a choice, consciously undertaken. It didn't fall on their laps, and in fact they went to great lengths over the course of Luther's and Melanchthon's lifetimes not only to reform the university in accord with it, but to defend it from the pretenders of obscurantism (Müntzer and those of his ilk) and the scholasticism which remained a powerful influence in late Medieval life.