The second aliyah continues to describe the procedure for purifying a person that is tamai mais. But here is mentioned the interesting fact that makes this the ultimate chok: that the ashes of the red heifer can make someone pure, but all the people involved in the manufacture and use of the ashes become impure from their involvement. This apparent contradiction is why this commandment is considered the biggest chok of all.
This aliyah then brings the story of the Jews' travels in the desert 38 years later to the 40th year in the desert, when the Jews stop in the wilderness of Tzin. It is here that Miriam, who was Moshe and Aharon's sister, passes away and is buried. Immediately after this, the Torah says the people had no water, and Rashi says that this is an indication that previous to Miriam's death, for 40 years, the Jewish community had plenty of water from a well provided because of Miriam's righteousness. The people start bitterly complaining about the lack of water to Moshe and Aharon.