The Book of Leviticus foreshadows the Mass and the new life in grace that Catholics are supposed to enjoy. Many don't because they do not understand what they have been given.
Leviticus is the third book of the Pentateuch -- The first five books of Scripture known as the Five Books of Moses -- The Torah. The name "Leviticus" is derived from the Septuagint, the Greek translation of Scripture into Greek by seventy elders in Alexandria. Even though the book seems to be addressed to the priests (the Levitical order), the book is addressed to all Israelites while living in the wilderness.
You shall be holy for I your God am holy (Leviticus 19:2)
This verse forms as it were the constitution of Israel. The call to holiness is at the heart of Leviticus and it is echoed in the gospels: "Be perfect for your heavenly Father is perfect" (Matthew 5:48) and "Be merciful for your heavenly Father is merciful" (Luke 6:36).
But Leviticus can be understood without the whole of Scripture. As Alfred Edersheim in his book "The Temple -- Its Ministry and Services" reminds us: "Moses must not be read independently of the Psalms, nor yet the Psalms independently of the Prophets. Theirs are not so many unconnected writings of different authorship and age, only held together by the boards of one volume. They form integral parts of one whole, the object of which is to point to the goal of all revelation in the appearance of the Christ. Accordingly, we recognize in the prophetic word, not a change nor a difference, but three well-marked progressive stages, leading up to the sufferings and the glory of Messiah. In the Proto-Evangel, as Genesis 3:15 has been called, and in what follows it, we have as yet only the grand general outlines of the figure. Thus we see a Person in the Seed of the woman; suffering, in the prediction that His heel would be bruised; and victory, in that He would bruise the serpent's head. These merely general outlines are wonderfully filled up in the Book of Psalms. The 'Person' is now 'the Son of David'; while alike the sufferings and the victory are sketched in vivid detail in such Psalms as 22, 35, 49, and 102; or else in Psalms 2, 72, 89, 110, and 118— to speak of other almost innumerable allusions."
Indeed, Leviticus begins where Exodus left off. There is a deep unity in Scripture that points to the unity of faith and the unity of the Liturgy for Leviticus is first and foremost a book on the Liturgy and Morality, and the sacrificial system it presents to us is a shadowy figure of the Mass. As we reflect on this book, we shall better understand the meaning of "Sacrifice" in our own lives. We will delve deeper into the Mass and realize the efficacy of the Lord's prayer in our lives. Leviticus is a window open on the holiness of the Lord. By contemplating its sacred verses we meditate on the great mystery of the one holy God who deigned walk in our midst and wished to be Emanuel -- God with us.