Feminism must be a daily practice because patriarchy is a daily affair. If the purpose of patriarchy is to break each of us into fragments, then feminism is the struggle to remain whole. We have to be whole people before we can give the best of ourselves to any purpose.
The best feminism comes out of an affection for the women in our lives. Once we orient ourselves toward our sisters and moms and friends and colleagues, we are not far from discerning the obstacle all women confront in the form known as patriarchy.
If patriarchy subjugates all women as a class, then it can only be challenged by advocating for all women as a class. This is the step we must take as men: to regard all women with the same concern we are taught to reserve for certain women.
Feminism is important for men because it teaches us to listen to women who have thought deeply about their own struggles, but also to provide encouragement to women who haven't. The influence men exert in many women's lives is constant, but the content of such influence is variable. If men aren't active in their fight against patriarchy, their influence does little to assist women who might be active in theirs.