Parshas Chukas begins by introducing us to the quintessential chok (a mitzvah whose meaning is not understood): The Red Heifer. The heifer was slaughtered and burned and its ashes were used to purify people who were tammei (impure), yet rendered the Priest who sprinkled them impure.

The parsha then skips ahead thirty eight years to describe events that occurred just before the Jews were to enter the Land of Israel. Miriam the Prophetess died and the Jews were left without water (a miraculous well had produced water in her merit as long as she lived). G-d commanded Moses and Aaron to speak to a particular rock and have it produce water; Moses struck the rock with his staff instead. As a punishment for not heeding G-d's word, G-d told both Moses and Aaron that they  would not enter the Land of Israel.

The Jews then proceeded toward the Promised Land. Moshe asked permission from the Edomites for the Jews to travel through their land. He was refused and the Jews  circumvented the kingdom. Later, he asked Sichon, the Emorite king, to travel through  his land. Not only did he refuse,  he went to war against the Jews and was soundly defeated. As they neared the kingdom of Bashan, Og, the Bashanite king who was a giant, prepared to wage battle against the Jews. G-d told Moshe not to worry, the Jews  would defeat Og.