Generally, a vow is a solemn promise voluntarily made to God to perform some act, make some offering, or enter some condition. Some suppose that Paul had his hair cut to fulfill a Nazirite vow. Yet, it should be noted that according to the Scriptures, on completing a period of special service to Jehovah, a Nazirite was to have his head shaved “at the entrance of the tent of meeting.” It would seem that such a requirement could be carried out only in Jerusalem and thus not in Cenchreae.—Num. 6:5, 18.
The Acts account says nothing regarding when Paul made his vow. It could conceivably have been made even before he became a Christian. The account is equally silent concerning whether Paul made any specific request of Jehovah. One reference work suggests that Paul’s having his hair clipped short could have been “an expression of thanksgiving to God for his protection, which had enabled [Paul] to complete his ministry at Corinth.”