Even if one gives up the concept of God, there are quite a few recognized immaterial things that one has to struggle with. Things such as thought, truth, logic, morality, purpose, and justice become a real problem if the universe is simply material. One could say that these things are imaginary, but then they would have to explain the immaterial construct of imagination.
Joel Furches, Christ-Centered Apologetics: Sharing the Gospel with Evidence
inspirational-religious, philosophy, philosophy-of-religion, theology