What roles do belief and action play in Judaism?  Is one more important than the other? Rabbi Menachem Kellner has a lot to say about this.  

The upshot of all of this is that Judaism is a religion which places a great deal of emphasis on correct behavior.  But Judaism is not simply a system of observances per se (a ‘religion of pots and pans’, as some of its detractors like to say).  One observes the commandments of the Torah, ideally, because of one’s relationship with God, out of love, with no thought of reward and punishment.  The commandments are not an end in themselves, in other words, but an expression of the Jew’s belief, emunah. In God. Trusting in God, and knowing what to do to give that trust concrete expression, the Jew has no need of subtle theological formulations and distinctions.  In a works-oriented religion like Judaism, emphasis on ‘belief in’ makes more sense than an emphasis on ‘belief that’: Judaism has thus always been more concerned with knowing that to do than with knowing what to think. (Menachem Kellner, Must a Jew Believe Anything?, pgs.45-46)

Deed over creed!  Does what I do impact what I believe?