In this Torah portion, Moses sends out twelve scouts (one from each tribe) to explore the Promised Land and make their report back to the Children of Israel. They are gone from the camp for 40 days, and when they return, their report is divided. Ten scouts report that the land is filled with giants who would be unconquerable, but Joshua and Caleb report that, with God's help, they could easily be defeated. The people listen to the ten scouts and panic, and lament, and wish aloud that they had never left Egypt.
God offers to Moses to kill all the Children of Israel and give Moses a better people to lead, but Moses asks God to reconsider. If the Children of Israel die in the wilderness, then the other peoples will see it as God's failure, not the failure of the Israelites. So God reluctantly spares their lives. It is notable that previously Abraham had argued with God when God insisted on killing outright whole peoples, but Moses actually managed to spare whole peoples from God's wrath.
Towards the end of the Torah portion is an interesting mitzvah that is used as the third paragraph of the Sh'ma prayer, which Jews recite morning and night every day. God commands the Israelites to wear tassels on the corners of their garments, and to twist into the tassels a single thread of blue wool, dyed with the blue dye called תכלת, or tekhelet. This dye came from an animal called the חילזון, or khilazon. This animal was most likely a sea snail. The Talmud explains that the animal lived in the Mediterranean Sea, and was shaped somewhat like a fish with a shell, and that its blood was the dye. It only surfaced every seventy years, so this dye was very rare and expensive. After the Romans expelled the Jews from Palestine, the knowledge of how to make tekhelet was lost. The Talmud also warns that plant indigo is the same color, but that using plant dies instead of genuine tekhelet is not kosher. The Radziner Rebbe in the 19th century had a vision that the Messiah visited him and told him that he had to discover how to make tekhelet in order for the Messiah to come. He moved to Palestine and spent decades researching the dye, and finally devised a dye prepared from cuttlefish that looks indigo blue. Another rabbi at the time, Rabbi Yitzhak HaLevi Herzog, analyzed the cuttlefish dye, and found that it was Prussian Blue, which can be synthesized by other sources, and therefore concluded that the cuttlefish was not the chilazon.
The famous murex snail of antiquity, which was the source of the Roman purple dye, was Rabbi Herzog's choice for techelet, even though the dye from the murex snail is purple instead of blue. This purple dye was incredibly expensive and rare, and was the only source of purple dye in antiquity, which is why only Roman emperors (and later kings) were allowed to wear it. Incidentally, the first synthetic purple dye was derived from coal-tar derivatives, and was called "mauve". The first garment dyed mauve was given as a gift to Queen Victoria, who wore it publicly as a testament to British industry.
In the 1980s, a scientist in Israel exposed murex dye to sunlight, and found that the sun broke down the chemicals in the dye and turned the purple dye indigo blue. It is currently thought that this is the true techelet. I own a prayer shawl with fringes, with one thread dyed using this dye. Ashkenazi Jews generally don't wear blue threads in their fringes, and Sephardic Jews often do, using this or the cuttlefish dye.
As a memento to the lost dye, Ashkenazi Jews wore prayer shawls with a blue stripe in them, and this blue stripe is also on the top and bottom of the flag of Israel. This blue is the reason why Craft Lodges in Freemasonry are called "Blue Lodges", and the royal murex dye is why Grand Lodge officers wear purple.