Then the priest shall present them before the LORD and shall offer his sin offering and his burnt offering.
What is interesting about this verse is that it describes the condition of ending a Nazirite vow. This was a special vow that a person could take to dedicate themselves uniquely to the Lord. They set themselves apart by not cutting their hair, refraining from wine and all products made of grapes (hard to do in a Mediterranean culture), and avoiding any potential contact with dead bodies of people or animals. It was a unique vow meant to help the person who took the vow concentrate on their relationship with the Lord. And the hairstyle made it visible to everyone else in the person’s life. The most notorious Nazirite in the Old Testament was Samson. But Paul in the the Book of Acts appears to have taken this kind of vow at one point.
What is interesting was that at the end of the time period of the vow (set by the person taking the vow) in addition to a haircut by the priest, the person also offered a sin offering along with additional offerings. Even though the vow was meant to concentrate on sanctification, the sacrifice of the vow was not enough to remove the guilt of the sin. They still did wrong things. The sin offering was meant to deal with that issue. The Nazirite vow then did not make them sinless, or even “more holy” than someone else, even though they were concentrating on God with an unusual fervor. God still had to atone for sin despite the efforts of the Nazirite.
Here is where I am going with this. God knew we have a tendency to trust in our efforts, and the Law, though it was good, by nature fed this in us. And the Nazirite rules were even more restrictive. It would be easy to think that keeping the rules made me holy. God made sure that was not the external emphasis for the Nazirites by insisting that sin offerings be part of the vow. The same principle holds true today. When we come to faith in Christ, we are saved by His work, not our own. And He keeps us holy, even as we are called to obey. I still must confess my sins. I still must seek forgiveness from God and those I may sin against. This will always be the case until I reside with God in heaven.