Christian are consecrated to the Lord

Numbers 6:1-21
If a man or woman wants to make a special vow, a vow of dedication to the Lord as a Nazirite, they must abstain from wine and other fermented drink and must not drink vinegar made from wine or other fermented drink. They must not drink grape juice or eat grapes or raisins.  As long as they remain under their Nazirite vow, they must not eat anything that comes from the grapevine, not even the seeds or skins.
During the entire period of their Nazirite vow, no razor may be used on their head.
Throughout the period of their dedication to the Lord, the Nazirite must not go near a dead body.  Even if their own father or mother or brother or sister dies, they must not make themselves ceremonially unclean on account of them, because the symbol of their dedication to God is on their head. Throughout the period of their dedication, they are consecrated to the Lord.
This is the law of the Nazirite who vows offerings to the Lord in accordance with their dedication, in addition to whatever else they can afford. They must fulfill the vows they have made, according to the law of the Nazirite.
A special vow gives the Nazirite (not to be confused with Nazarene, some one from Nazareth) his or her spiritual status. The outward marks of consecration to God are:

• No wine or strong drink ( the priests were forbidden this too, as part of fitting themselves to approach God; it may also reflect a commitment to nomadic(游牧) simplicity,over against the 'corrupting' influences of civilization):
• Uncut hair;
• Special care to avoid defilement through contact with a dead body

The vow was usually for a limited time, but Samson had a lifelong vow. Samuel may also have been a Nazirite. 
It is not known how or when these practises originated, but Nazirites continued to feature on through the exile to New Testament times.
Why?
Nazirite means a man or woman belong to the Lord for limited period, they are dedicated to the Lord, so they have to keep away wine and dead body, and uncut hair. For God is holy, 
The head of man is the glory of the Lord, so they uncut hair.
How?
How about a Christian, should keep away from the custom of the world, we are consecrated to the Lord