A chok is a commandment that a human can not find a reason for, as opposed to a mishpat, which is a commandment that a human being might think up himself. To not murder, for example is a mishpat. One reason this parsha is called Chukas is because it deals with the ultimate chok, the "para aduma", the red heifer. King Solomon was said to be the wisest person who ever lived, but even he couldn't rationalize the seeming contradictions in this commandment.

The Rambam says that there have been nine red heifers found and used so far in Jewish history, and the tenth will be used when Moshiach comes to purify the generation of the redemption, may it happen speedily in our days.

• This first aliyah gives instructions that a completely red cow (the para duma) is to be slaughtered, and burnt, and its ashes saved. Then, when a person becomes tamai mais (impurity from a dead body), a procedure is described here where such a person is purified on the third and seventh day with the ashes of the para duma, and after that, he is tahar (pure).
  
  
• 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.
  
  
• After the complaints of thirst for water of the Jewish people in the previous aliyah, in this, the third aliyah, G-D tells Moshe and Aharon to take a staff and gather the people together before a certain rock. They should speak to the rock in front of everybody, and it would give forth water. Moshe and Aharon do gather everybody, but instead of speaking to it as commanded, Moshe strikes the rock twice and it gives forth water.
  
  G-D says to Moshe and Aharon that, since they didn't sanctify G-D in the eyes of all the Jews, they won't bring the Jews into Israel. Rashi says that had they spoken to the rock and it had brought forth water, the Jews would have reasoned that if the rock, which doesn't speak or hear nor does it require anything to exist, does what G-D wants by bringing forth water, then certainly should we. The Torah then says that these are the waters of Maribah. Rashi points out that this is what Pharaoh's astrologers saw back in Egypt when they saw that the leader of the Jews would be smitten by water, and they then decreed that all the baby boys should be thrown into the river.
  
  
• In the fourth aliyah Moshe sends messengers to the King of Edom asking permission to pass through his land. He promises to not harm the land in any way. And moreover he promises to purchase food and drink from them despite the fact the Jews are self-sufficient with their manna and because of this the Edomites should benefit. However, the King of Edom replies that they may not pass through, and that he will come out with a sword to prevent them. To this Israel turns away in their travels.
  
  
• After turning from Edom, in this, the fifth aliyah, the Jews arrive at Mt. Hor. Rashi says that even though the Clouds of Glory that led them in their journeys also leveled mountains for them, three mountains remained standing: Mt. Sinai for the giving of the Torah, Mt. Hor for the burial of Aharon, and Mt. Nevo for the burial of Moshe. At G-D's command, Moshe and Aharon and Aharon's son Elazar go up the mountain. Then Moshe takes the clothes of the Kohane Gadol (High Priest) off of Aharon and puts them on Elazar. After Aharon sees that his son is taking over the office of Kohane Gadol, Aharon passes away. When Moshe and Elazar come down the mountain without Aharon, the people understand that Aharon has passed away, and mourn 30 days. Rashi says that all the people wept because they loved Aharon because he would always pursue peace, and strive for peace between men and between a husband and his wife. After Aharon passes away, Rashi says that the Cloud of Glory departed from the Jews. The nation of Amalak hears this and attacks the Jews, but G-d causes the Jews to win.
  
  
• The sixth aliyah then describes more journeys of the Jews in the desert. Also in this aliyah, another great miracle is performed, comparable to the splitting of the Yam Suf. The Jews approach the valley of Arnon. This valley is very deep and narrow. Rashi says that the mountains are so close that a man on each of the two facing mountains could speak to one another. The Emorim realize that this is an excellent place to ambush the Jews because the Jews have to pass in a narrow space far below them. So the Emorites take ammunition and station themselves in crevices and caves on each mountain ready to hurl rocks on the Jews below. As the Jews pass, the mountain on the Emorite side (which later was to become part of Israel) trembles with awe at the approach of the Aron Hakodesh and leans toward the other mountain. The mountains come together and the peaks of one mountain precisely enter the caves of the other, crushing the Emorite army hiding there.
  
  
• In the seventh aliyah the Jews approach the land of Sichon and send a message to its king asking permission to pass through in peace. The King refuses and comes out with an army to attack the Jews. The Jews fight them and win, and occupy their land. Later the king of Bashan, named Og, attacks the Jews. As a result the Jews kill King Og and occupy his land also.
  
  At this point the Jewish nation has reached the bank of the Jordan River, just across from the city of Jericho in the land of Israel.