This Book of the Torah is so called because its actions and laws take place in the desert. The barren desert is strange place for Hashem to give His laws to the B’nei Yisrael. Hashem chose to give the laws to a new nation because they had not had time to become set in their ways and would be able to accept the direction of a new leader. Also, giving the laws in the desert, a barren place devoid of permanent homes and any luxuries, meant that the people would be willing to accept the guidance of Hashem. They would come out of the desert free from the influences of other nations. In the same way a Torah scholar should consider himself as a midbar, retaining his Torah spirit and being uncorrupted by alien social influences.
The sedra of Bamidbar is always read on the Shabbat before Shavuot. The simple reason for this is to make a separation between the curses read in the previous sedra, Behukatai, and the giving of the Torah. It is a preparation for us to receive the Torah. The sedra deals with the laws and history of the Mishcan, Tabernacle. Ramban, Nachmanides, suggests that the Mishcan, and later the Temple, was to serve as the permanent home on earth for Hashem. The Mishcan and the Temple became a focal point for the Jewish people as the place where they could be nearest to Hashem.
The Book of Bamidbar starts with a census of all males over 21. Why yet another census? Rabbi Yishaya Halevi Horowitz says that by counting, Hashem wanted the Jewish people to last forever and not be beaten by all the other nations of the world. Ramban gives 3 reasons: a) to show how quickly the nation of B’nei Yisrael grew; b) each member of the nation could come before Moshe and Aharon to be counted as a person of worth, to be blessed and their half shekel contribution would bring them atonement; c) the census was needed to ascertain numbers for the military campaign and how many people would have the right to receive portions in land.
The sedra of Bamidbar also gives the order in which the tribes should accompany the Mischan when travelling in the desert. The Mishcan would be in the centre and the twelve tribes divided into four units surrounding it, as protection.