Charles Ellicott Commentary Acts 21:24

"these take, and purify thyself with them, and be at charges for them, that they may shave their heads: and all shall know that there is no truth in the things whereof they have been informed concerning thee; but that thou thyself also walkest orderly, keeping the law." — Acts 21:24 (ASV)

Purify yourself with them . . .—This involved sharing their abstinence for the uncompleted term of the vow, and shaving the head at its conclusion.

Pay their expenses . . .—Literally, spend money on them. This involved payment, first, for the act of shaving the head, for which there was probably a fixed fee to a priest or Levite; and second, for the sacrifices which each Nazarite had to offer—namely, two doves or pigeons, a lamb, an ewe lamb, a ram, a basket of unleavened bread, a meat offering, and a drink offering (Numbers 6:9–12).