Charles Ellicott Commentary Acts 21:23

"Do therefore this that we say to thee: We have four men that have a vow on them;" — Acts 21:23 (ASV)

We have four men which have a vow on them.—The advice was eminently characteristic.

1. It came from one who himself lived as bound by the Nazarite vow. “No razor came upon his head, and he drank neither wine nor strong drink” (Hegesippus in Euseb. Hist. ii. 23). By connecting himself with such a vow St. Paul would show that he was content in these matters to follow in the footsteps of St. James, that he looked upon the observance of the Nazarite vow, if not as binding, at any rate as right and praiseworthy.
2. It is obvious that St. Paul’s conduct on his last visit to Jerusalem had furnished a precedent for the line of action now recommended.

He had then come as a Nazarite himself; had in that character burnt the hair which he had cut off at Cenchrea (see Note on Acts 18:18), and had offered the accustomed sacrifices.

Why should he not repeat the process now? There was, however, this difficulty: the minimum period of the Nazarite vow was for thirty days, and as St. Paul had not taken the vow previous to the advice, and probably wished to leave Jerusalem soon after the feast was over (Acts 19:21), it was out of his power to fulfil it now in its completeness.

Jewish usage, however, made an intermediate course feasible. A man might attach himself to a Nazarite, or company of Nazarites, join in the final process of purification, which lasted, probably, for seven days (Numbers 6:9), shaving his head, and offering sacrifices with them.

This was considered in itself a devout act, especially if the newcomer defrayed the cost of the sacrifices. Agrippa I, for instance, had in this way gained credit with the Jews, as showing his reverence for the Law (Jos. Wars, ii. 15, § 1).

It is clear that the four men were members of the Church of Jerusalem, and the fact is interesting as showing how intensely Jewish that church still was in its observances.