If Martin Luther's assumptions on faith in the Word of God are correct, then humanity has nothing to doubt. But his skepticism of the Catholic Church is not a complete philosophical skepticism: at no point in his work is the notion of God questioned. Descartes does question the existence of God, but after answering his skeptical objections he is able to prove God's existence. Since God exists and is the perfect being, he reasons in his fourth meditation that therefore I acknowledge that it is impossible for God ever to deceive me, for trickery and deception is always indicative of some imperfection (Meditations on First Philosophy 81). Luther says that one thing, and only one thing, is necessary for Christian life, righteousness, and freedom. That one thing is the most holy Word of God (The Protestant Reformation 7). Descartes would probably acknowledge that the Word of God exists, but it is difficult to tell if he would accept that it came from God.
[...] He simply questions the existence of God, concludes that God exists and after some side remarks leaves the matter as it is. Descartes seems to fulfill exactly what Luther was recommending about faith. Luther stresses throughout his treatise that for the Christian life faith is necessary, not works. Descartes resolves his question with that very thing: a faith in God, and does not bother about the moral consequences. Of course if Descartes has proven the existence of God, he is claiming to actually know that God exists, not just to have some strong belief. [...]
[...] But he still makes further deductions about God even though he has not addressed the existence of God and submitted it to an intellectual and skeptical examination. In other words, he could be making an error if his initial assumption is wrong. But if he is making an error, then he is deceived according to Descartes, but since Luther is talking about a perfect God who by definition does not deceive, how can he be deceived? Luther isn't making a Cartesian error however. [...]
[...] Even if the Word of God is possibly the creation of erring human minds, both Luther and Descartes seem to be talking about the same God who is perfect and does not deceive. Descartes says that initially he doubts the very existence of God. He is talking about a concept, which has existed before him, and which he did not think up, later he does not invent a new definition of God but instead he justifies the commonly held belief, which he initially questioned. [...]
[...] For those who ask “What then is the Word of (Protestant Reformation Luther answers that it is gospel of God concerning His Son, who was made flesh, suffered, rose from the dead The Word of God is in fact, the first text to introduce this and many other notions about God, there is no text previous to the Word of God where God is defined so explicitly. The redemption given by Christ and other things described by the “many words of (Protestant Reformation do not exactly go against anything in Descartes' meditations; Descartes simply does not mention them. [...]
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