The name of the Parshah, "Chukat," means "Statute" and it is found in Numbers 19:2.
Moses is taught the laws of the red heifer, whose ashes purify a person who has been contaminated by contact with a dead body.
After forty years of journeying through the desert, the people of Israel arrive in the wilderness of Zin. Miriam dies, and the people thirst for water. G‑d tells Moses to speak to a rock and command it to give water. Moses gets angry at the rebellious Israelites and strikes the stone. Water issues forth, but Moses is told by G‑d that neither he nor Aaron will enter the Promised Land.
Aaron dies at Hor Hahar and is succeeded in the high priesthood by his son Elazar. Venomous snakes attack the Israelite camp after yet another eruption of discontent in which the people “speak against G‑d and Moses”; G‑d tells Moses to place a brass serpent upon a high pole, and all who will gaze heavenward will be healed. The people sing a song in honor of the miraculous well that provided them water in the desert.
Moses leads the people in battles against the Emorite kings Sichon and Og (who seek to prevent Israel’s passage through their territory) and conquers their lands, which lie east of the Jordan.
Learn: Chukat in Depth
Browse: Chukat Parshah Columnists
Prep: Devar Torah Q&A for Chukat
Read: Haftarah in a Nutshell
Play: Chukat Parshah Quiz
Why was Aaron also punished for Moses striking the rock?
Moses and Aaron worked together as a team (Aaron being Moses's interpreter, among other duties). In the episode of striking the rock, Aaron could have intervened and prevented Moses from striking the rock, or at least kept the crowds at bay while Moses figured out what needed to be done.