The Book of Numbers is the fourth book of the Bible. It continues the story of Moses and adds to the Mosaic Law. The book is called Numbers because it contains information on the censuses supposedly carried out at the time.
Origins of the book
The book most likely did not have one author, but several. Christians and Jews claim that Moses wrote Leviticus together with the other five so-called Books of Moses, although unlikely. In the 18th Century Thomas Paine made obvious the problems with this claim...
But granting the grammatical right, that Moses might speak of himself in the third person, because any man might speak of himself in that manner, it cannot be admitted as a fact in those books, that it is Moses who speaks, without rendering Moses truly ridiculous and absurd:--for example, Numbers 12:3 "Now the man Moses was very MEEK, above all the men which were on the face of the earth." If Moses said this of himself, instead of being the meekest of men, he was one of the most vain and arrogant coxcombs; and the advocates for those books may now take which side they please, for both sides are against them: if Moses was not the author, the books are without authority; and if he was the author, the author is without credit, because to boast of meekness is the reverse of meekness, and is a lie in sentiment. 
- God led the Israelites through the desert by appearing as a cloud by day and a flame by night.
- God repeatedly commits massacres against his people when they complain about being hungry, about Moses's leadership, or about his monopoly on speaking with God.
- Moses's siblings (Aaron and Miriam) criticize him for marrying an Ethiopian woman. God gives Miriam leprosy for a while as punishment.
- God tells the Israelites they must wander the desert for forty years because they were afraid of giants that reportedly lived in the promised land.
- Moses and Aaron are told by God that they will not enter the promised land, because they miraculously get water from a rock by striking it, rather than by asking nicely.
- The Israelites and God together destroy whole cities and whole peoples.
- The Moabites hire a prophet named Balaam to curse the Israelites, but after Balaam's donkey talks to him and he sees an angel, he blesses the Israelites instead.
- God commands massacres against his people when they marry women from other tribes and begin sacrificing to their gods.
- But He later allows them to keep the virgins from some conquered cities, insisting that they first kill all the non-virgins and their male children.
Upon Critical Reading...
Numbers 31 contains the best example of immorality in the bible. Short version: God tells Moses to send 1000 of his people from each tribe (adding up to 12-14 thousand) to go kill another entire tribe, but to spare the virgin women, and keep them for themselves, along with all the processions of the other tribe. However, the men bring back all the children and all the non-virgin women. The men are then ordered to kill all the non-virgin women and the male children. The final number of the virgin women? 32,000 . A population of more than 300,000 would be needed to obtain this many virgins. So moral, you feel yourself becoming more murderous just by reading it!