All in, All the Time
When Bnei Yisrael say Naaseh V'Nishma they submit in totality to God, no questions asked. Rebbe Nachman: how is it possible to do anything before knowing what it is? The Jews don't say "we will do" before they hear anything; they say "whatever Hashem says, we will do and listen". If then, what is the novelty in נעשה ונשמע? The word נעשה means we will do God's will right away even if we doesn't understand it; afterwards "נשמע" - we will attempt to understand. נעשה, doing with complete faith, brings one to נשמע.
Provided courtesy of rabbisilber.com