This is the law of the Nazarite who hath vowed, and of his offering unto the LORD for his separation, beside that that his hand shall get: according to the vow which he vowed, so he must do after the law of his separation. This is the law of the Nazarite - We learn from Maimonides, in his Treatise of the Nazarite, that a man might become a Nazarite in behalf of another; that is, might assist him in bearing the expenses of the sacrifices, etc. "A son may fulfill the vow his deceased father hath made, but did not live to accomplish: - He that saith, upon me be the shaving of a Nazarite, he is bound to bring the offerings of shaving for cleanness, and may offer them by the hand of what Nazarite he will. If he say, Upon me be half the oblations of a Nazarite, then he bringeth half the offerings by what Nazarite he will, and that Nazarite payeth his offerings out of that which is his."
"By this," says Mr. Ainsworth, "we may see the reason of that which James said to Paul, though he had no Nazarite's vow upon him: 'We have four men who have a vow on them; them take and sanctify thyself with them, and Be At Charges With Them, that they may shave their heads, etc. Then Paul took the men, and the next day, sanctifying himself with them, entered into the temple to signify the accomplishment of the days of sanctification, (or Nazariteship), until that an offering should be offered for every one of them;' see Acts 21:23-26. For though Paul had not vowed or fulfilled a Nazariteship himself, yet might he contribute with them, and partake of their charges about the sacrifices."