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 xii. 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.