Existence

When Luther was younger he was taught by at least one Nominalist professor, Johann Nathin at the University of Erfurt. Here Luther came to dislike strongly the use of philosophy in theology. Luther's objection to this scholasticism was that Nominalists and existentialists had a Pelagian or semi-Pelagian view and Realists tended toward Gnosticism.

     Brecht, Martin. Martin Luther: His Road to Reformation, 1483–1521. Translated by James L. Schaaf. Philadelphia, 1985. Originally published in German: Martin Luther: Sein Weg zur Reformation, 1483–1521, Stuttgart, 1981

It would be easy to get discouraged in the world if the above were the only options available. While studying philosophy can be fun, Luther is correct that it should not be used in theology. It is easy to see how many churches (historical and modern) have gone wrong by adopting some of these philosophies.