Throughout the book of Levitcus God describes to Moses how the priests should be cleansed, dressed, atoned, etc, etc. Many of the descriptions are for the duties of the priests and their interaction with the Hebrew people. Chapter 21 describes rules specifically for the priests themeselves. The priests could not shave their heads or the edges of their beards. They could not cut their bodies. They must not marry certain women who were defiled by prostitution, or had been divorced. And throughout this chapter the reason God gives to Moses for these regulations is because the priests are "to be considered holy, because I the Lord am holy -- I who make you holy."
Now let's fast forward to the New Testament. 1 Peter 2 reads:
9But you are a chosen people, a royal priesthood, a holy nation, a people belonging to God, that you may declare the praises of him who called you out of darkness into his wonderful light. 10Once you were not a people, but now you are the people of God; once you had not received mercy, but now you have received mercy.
11Dear friends, I urge you, as aliens and strangers in the world, to abstain from sinful desires, which war against your soul. 12Live such good lives among the pagans that, though they accuse you of doing wrong, they may see your good deeds and glorify God on the day he visits us.
Now look at the first verses of 1 Peter and see who Peter is writing to:
1Peter, an apostle of Jesus Christ,
To God's elect, strangers in the world, scattered throughout Pontus, Galatia, Cappadocia, Asia and Bithynia, 2who have been chosen according to the foreknowledge of God the Father, through the sanctifying work of the Spirit, for obedience to Jesus Christ and sprinkling by his blood:
Grace and peace be yours in abundance.
Here is what Peter is saying... Jesus is the high priest and you are set apart as priests also. You see when Jesus shed his blood he was not only the sacrifice, but also the priest who offered the sacrifice on our behalf. Now we can become a royal priesthood, a holy nation, a people belonging to God.
Are you with me? Do you think that God still has rules for His priests? Shouldn't we be living like priests? Shouldn't we be holy? According to Leviticus priests should be considered holy, "because I the Lord am holy -- I who make you holy." Right? Here's how Peter says it:
13Therefore, prepare your minds for action; be self-controlled; set your hope fully on the grace to be given you when Jesus Christ is revealed. 14As obedient children, do not conform to the evil desires you had when you lived in ignorance. 15But just as he who called you is holy, so be holy in all you do; 16for it is written: "Be holy, because I am holy."