It can be helpful for understanding the meaning of terms in relationship and contrast to what they are not. I've come to distinguish the following sets of terms as opposites:
lies ~ truth
faith ~ reason
theism ~ atheism
religion ~ philosophy
ignorance ~ knowledge
Atheism does not necessarily imply a belief system, but it is an essential part of a comprehensive belief system for living in a world in which mysticism and religion have and continue to have a profoundly devastating influence on events which affect our lives.
If religion has proven anything, it is that the desire to fight the 'good fight' is simply not enough. One must first learn to understand and distinguish the difference between what is good and what is evil, which is in essence what the 'good fight' is all about. For until one knows what it is one truly knows and how, one can only guess as to whether or not one is one's own worst enemy in the battle for truth and good and to insure that reason prevails.