Numbers 6 lists the requirements for the Nazarite vow. From Scripture we know that there were at least three important Biblical figures that have taken the Nazarite vow. They were Samuel, Samson, and John the Baptist. Others, such as Paul may have taken a temporary Nazarite vow.

Acts 18:18
Paul stayed on in Corinth for some time. Then he left the brothers and sailed for Syria, accompanied by Priscilla and Aquila. Before he sailed, he had his hair cut off at Cenchrea because of a vow he had taken.

Lev 27:10a
Don't exchange or substitute animals, a good one for a bad one or a bad one for a good one.
Jesus was quick to demonstrate how dishonest it was to substitute sacrificial animals in the temple area for profit.
John 2:14-15
And He found in the temple those who sold oxen and sheep and doves, and the money-changers sitting. And when He had made a scourge of small cords, He drove them all out of the temple, also the sheep and the oxen. And He poured out the money-changers' money and overthrew the tables.

Leviticus and Deuteronomy list rules pertaining to vows of dedication.
Deut 23:21-23
If you make a vow to the LORD your God, do not be slow to pay it, for the LORD your God will certainly demand it of you and you will be guilty of sin. But if you refrain from making a vow, you will not be guilty. Whatever your lips utter you must be sure to do, because you made your vow freely to the LORD your God with your own mouth.
Some have stiff punishment for not fulfilling a vow that has been made. Just ask Jephthah.
Judg 11:30-35
And Jephthah made a vow to the LORD: "If you give the Ammonites into my hands, whatever comes out of the door of my house to meet me when I return in triumph from the Ammonites will be the LORD's, and I will sacrifice it as a burnt offering." Then Jephthah went over to fight the Ammonites, and the LORD gave them into his hands. He devastated twenty towns from Aroer to the vicinity of Minnith, as far as Abel Keramim. Thus Israel subdued Ammon. When Jephthah returned to his home in Mizpah, who should come out to meet him but his daughter, dancing to the sound of tambourines! She was an only child. Except for her he had neither son nor daughter. When he saw her, he tore his clothes and cried, "Oh! My daughter! You have made me miserable and wretched, because I have made a vow to the LORD that I cannot break."

Lessons to be learned here???

Certain mixtures are listed in the laws of separation as forbidden.  While we may not understand why these mixtures are forbidden, it gives us an indication of how God feels about Believers.  He says. "Be holy because I, the Lord your God am holy."  That's telling us that we need to keep ourselves away from unholy living, acting, speaking, thinking, hearing, etc.