In this week's parsha, when Moshe calls for those who are with Hashem to kill all of those who participated in worship of the golden calf, only the tribe of Levi approaches)לב:כו( . Presumably, Moshe expects that the other eleven tribes will be killed, indicating a clear separation between those who stray from Hashem and those who are with Him one hundred percent. What does happen, though, is that only one tribe (Levi) comes to Moshe, yet only three thousand of Bnei Yisrael are killed. What about the rest of Bnei Yisrael? Apparently, most of them are not sure where they stand in terms of accepting Hashem as God. They couldn't seem to decide between Hashem and (lehavdil!)
the golden calf, being skeptical enough of the golden calf that they will have no part in it, but not being confident enough in Hashem to obey Moshe's directive to kill those who did participate in the sin.
The Netziv interprets this event differently. He points out that most of our nation did not worship the golden calf (witness the fact that only three thousand people were killed for worshipping the golden calf). The rest of them were not unsure of their beliefs; they were basically dedicated to Hashem. However, they were not totally perfect. Moshe asked for the assistqance of those who were totally dedicated to God. Only persons entirely dedicated to God would merit divine protection in their battle against those who worshipped the golden calf.