Leviticus the third book of the Torah, as well as being the third book in the Tanakh, the Hebrew Bible (known to Christians as the Old Testament).; so called in the Vulgate, following the Septuagint, because it treats chiefly of the Levitical (priestly) worship.
In the first section of the book (1-17), which exhibits the worship itself, there is,
(1.) A series of laws (1-7) regarding sacrifices, burnt-offerings, meat-offerings, and thank-offerings (1-3), sin-offerings and trespass-offerings (4; 5), followed by the law of the priestly duties in connection with the offering of sacrifices (6; 7).
(2.) An historical section (8-10), giving an account of the consecration of Aaron and his sons (8); Aaron's first offering for himself and the people (9); Nadab and Abihu's presumption in offering "strange fire before Jehovah," and their punishment (10).
(3.) Laws concerning purity, and the sacrifices and ordinances for putting away impurity (11-16).
An interesting fact may be noted here. Canon Tristram, speaking of the remarkable discoveries regarding the flora and fauna of the Holy Land by the Palestine Exploration officers, makes the following statement:, "Take these two catalogues of the clean and unclean animals in the books of Leviticus  and Deuteronomy . There are eleven in Deuteronomy which do not occur in Leviticus, and these are nearly all animals and birds which are not found in Egypt or the Holy Land, but which are numerous in the Arabian desert. They are not named in Leviticus a few weeks after the departure from Egypt; but after the people were thirty-nine years in the desert they are named, a strong proof that the list in Deuteronomy was written at the end of the journey, and the list in Leviticus at the beginning. It fixes the writing of that catalogue to one time and period only, viz., that when the children of Israel were familiar with the fauna and the flora of the desert" (Palest. Expl. Quart., Jan. 1887).
(4.) Laws marking the separation between Israel and the heathen (17-20).
(5.) Laws about the personal purity of the priests, and their eating of the holy things (20; 21); about the offerings of Israel, that they were to be without blemish (22:17-33); and about the due celebration of the great festivals (23; 25).
(6.) Then follow promises and warnings to the people regarding obedience to these commandments, closing with a section on vows.
The various ordinances contained in this book are said to have been delivered in the space of a month (comp. Ex. 40:17; Num. 1:1), the first month of the second year after the Exodus. It is the third of the five books of Moses.
Orthodox Jews believe that this entire book is the word of God, dictated by God to Moses on Mount Sinai. See also JEDP theory.
After the Christian era began, parts of this book began to be seen as prophecy of the coming of the Christian messiah, Jesus Christ. To Christian readers, Leviticus is literally about Jewish law and regulations for worship, but is in fact coded prophecy that is made clear in the Epistle to Hebrews. It is said to contain in its law the gospel of the grace of God, although no one before the time of Jesus was able to notice this.