Judaism is an action-oriented religion. We have, according to the Talmud, 613 Commandments — not just a top-10 list. In rabbinic courts, your actions can be praised or punished. Faith is a means to achieve just ends, prayer as a way of connecting to the Source of Creation so that we can better play our part in its ongoing unfolding.
But what if you can achieve those same just, creative, Jewish ends without faith as a means or a motivation? Do you need God if you observe the 613 Commandments (or reinterpret and reapply them as so many modern Jews do)? Do you need God if you consider prayer an act of introspection — one that changes the way you understand your actions, much as your believing counterparts do? Do you need God if you love the Torah as a national treasure of the Jewish people — but one written and conceived of by our ancestors rather than the Divine?