This week's section is called Korah. It's the name of a cousin of Moses who led a rebellion against him. Moses was the king, so to speak; his brother Aaron was the High Priest; and Elzaphan (another cousin of both) was the leader of the Kohathim family, a family of the tribe of Levi to which Korah also belonged. Essentially, the rebellion stemmed from Korah's desire for a position of power in governing the Jewish people.
In the end, the rebellion is quelled, and Korah, along with all his followers, is swallowed up by the earth. But before this happens, Moses has a very interesting exchange with God. First, God proposes to Moses that he destroy all the rebels (see Numbers 16:20-22 and Rashi's commentary), to which Moses responds by pointing out the difference between a king of flesh and blood and God: a king of flesh and blood, when some of his court sin, doesn't know who sinned, so he punishes everyone, while God, who knows all people's thoughts, does know the true sinner. So, Moses concluded, why punish the innocent? In response to this argument, God tells Moses that He will indeed reveal who sinned and who did not.
Now, why did Moshe begin by speaking of "part of his court (plural)" and end by speaking of "who sinned (singular)?" Furthermore, since Korah appears to be the only sinner, why did Moshe use the example of the king's court sinning, which involves more than one person?
The answer to these questions is that there are two levels of participation in the rebellion: Korah and his followers. Korah himself was the instigator of the rebellion, who convinced (along with Dathan and Abiram, as we will see later) 250 tribal and family leaders to follow them in rebelling against Moses' authority. His followers, on the other hand, were merely seduced by Korah's promises of justice. This does not mean that being seduced by Korah excuses them from the corresponding punishment for their wrongdoing, but they certainly cannot be considered in the same category as Korah.
One more fact, and a lesson: Moses thought there was only one instigator (Korah), while God indicated that there were actually three: Korah, Dathan, and Abiram (see Numbers 16:24). Regarding the latter two, Moses tried to talk to them before the rebellion escalated, but they refused, and not only that, but they answered him arrogantly and insolently. Here we can see the extent to which people should be judged fairly: even after Dathan and Abiram publicly disrespected him, Moses did not consider them "sinners" or instigators of the rebellion along with Korah. That is why he told God that "He (God) knew who (in the singular) the sinner was." We should learn from Moses to judge others favorably.