Vayikra is a book that is concerned with the holy and the profane; the pure and the impure.  Nearly every mitzvah in Vayikra contains these categories.  The Jewish people are told that they are to be kadosh because God is kadosh.  In Vayikra, it is the holy that is the primary pathway to God.  The mishkan (tabernacle), the center of holiness on earth, is the pathway for that connection.