Setting apart of the Levites

Numbers 8:5-26
To purify them, do this: Sprinkle the water of cleansing on them; then have them shave their whole bodies and wash their clothes. And so they will purify themselves.
In this way you are to set the Levites apart from the other Israelites, and the Levites will be mine.
Aaron is to present the Levites before the Lord as a wave offeringfrom the Israelites, so that they may be ready to do the work of the Lord. 
 They are the Israelites who are to be given wholly to me. I have taken them as my own in place of the firstborn, the first male offspring from every Israelite woman. Every firstborn male in Israel, whether human or animal, is mine. When I struck down all the firstborn in Egypt, I set them apart for myself. And I have taken the Levites in place of all the firstborn sons in Israel.
Men twenty-five years old or more shall come to take part in the work at the tent of meeting,  but at the age of fifty, they must retire from their regular service and work no longer.
Those who serve God must be clean through and through. Washing and shaving ensure outward cleanliness. The blood of sacrifice cleans the inward stain of sin.
Way?
To serve the Lord have to claen through water and inward stain of sin.
Levites was chosen as first born of Israelites, so they may do the work of the Lord.
To be a God's servant needs may requirement for God is Holy.
How?
Clean myself and keep away from the unclean things, For I am a Christian, should live like Jesus Christ.