This was the kind of vow where the person would not drink alcohol or cut their hair until the end of the set period of time. Alternate translation: "four men who made a promise to God".
## pay their expenses for them ##
The expenses would go towards buying a male and female lamb, a ram, and grain and drink offerings. Alternate translation: "pay for what they will need."
## keep the law ##
"live a life that conforms to the Law of Moses and other Jewish customs"