Why take the Nazarite vow?

And the Lord spake unto Moses, saying,  Speak unto the children of Israel, and say unto them, When either man or woman shall separate themselves to vow a vow of a Nazarite, to separate themselves unto the Lord :  He shall separate himself from wine and strong drink, and shall drink no vinegar of wine, or vinegar of strong drink, neither shall he drink any liquor of grapes, nor eat moist grapes, or dried.  All the days of his separation shall he eat nothing that is made of the vine tree, from the kernels even to the husk.  All the days of the vow of his separation there shall no razor come upon his head: until the days be fulfilled, in the which he separateth himself unto the Lord , he shall be holy, and shall let the locks of the hair of his head grow.
Numbers 6:1-5

A Nazarite or Nazirite is one who is set apart and voluntarily gives up certain things during the period of the vow in order to live in holiness to God. A man or woman could take the vow. The vow is usually for a specific period.
The first thing a Nazarite gives up is alcohol. The Nazarite will also not eat anything from the vine tree- grapes and will not cut the hair not even with razor until the vow is fulfilled.

The major reason for the vow is to separate themselves unto God. Without holiness no man shall see the Lord. Among those who took the vows were Samuel, Samson, John the Baptist, Apostle Paul.

Although the Nazarite vow is an Old Testament concept, there is a New Testament parallel to the Nazarite vow. In Romans 12:1-2 Paul states, “Therefore, I urge you, brothers, in view of God's mercy, to offer your bodies as living sacrifices, holy and pleasing to God—this is your spiritual act of worship. Do not conform any longer to the pattern of this world, but be transformed by the renewing of your mind. Then you will be able to test and approve what God's will is—his good, pleasing and perfect will.” For Christians, the ancient Nazarite vow symbolizes the need to be separate from this world, a holy people consecrated to God (2 Timothy 1:9; 1 Peter 1:15).