Awhile ago I had written a blog concerning Paul’s vow, and it can be found HERE. Paul’s vow and his second recorded missionary journey end about the same time. After leaving Corinth with a brief visit to the synagogue at Ephesus in the province of Asia (Acts 18:19), Paul sailed off to Caesarea and went up (to Jerusalem) to report to the church there and offer the appropriate sacrifices pertaining to his vow (Acts 18:21-22; cp. 21:17-19 and 23-24, 26-27).
Luke tells us that Paul ‘cut’ his hair while at Cenchrea, the eastern port of Corinth bordering the Adriatic Sea, because he had a vow (Acts 18:18). He doesn’t say how long Paul had taken the vow, nor does he say why Paul made a vow. However, we may be able to understand the answers to these questions by drawing hints from the text. For example, when Paul broke off fellowship with the synagogue at Corinth the KJV renders Acts 18:6, “I am clean: from henceforth I will go to the gentiles.” In other words, Paul was saying he is innocent of any judgment their actions would bring upon them (cp. Ezekiel 33:4). In fact, Luke records Paul using the same Greek word, katharos (G2513), in this sense a few years later at Miletus where Paul told the elders of the Ephesian church that in preaching the Kingdom of God to them, he was “pure from the blood of all” (Acts 20:26).
Paul’s reply to the Jews in Acts 18:6 could be in answer to their blaspheming the Way or, viewed another way, could be in response to the Jews rejecting Paul’s testimony that he had indeed seen the resurrected Jesus. If the latter is true, Paul may have been led to take an oath calling God to witness that he had seen Jesus alive while Paul was near Damascus. The Jews’ continued rejection would not have left Paul exempt from his vow. He would have let his hair grow as a testimony against the unbelieving Jews. In this way, though Paul had left the fellowship of the synagogue, as long as he was in Corinth he would be passively preaching to his unbelieving brethren that the Kingdom of God had arrived, and this, that is Jews and gentiles coming together in common fellowship under the Lordship of Jesus, is what that Kingdom looks like.
If the above is logically true, then Paul’s vow was begun about the same time he separated himself from his unbelieving Jewish brethren and the synagogue at Corinth. For over a year it would have been a public testimony to them of their unbelief in the arrival of God’s Kingdom, and the coming judgment upon their nation, if they continue to reject God’s work. Paul’s shaving his head in verse-18 would again be a public statement, understood by all his Jewish brethren, showing his intention to offer his locks with the appropriate sacrifice on the altar at Jerusalem. In other words, Paul had not rejected his Jewish traditions by leaving the synagogue to preach Jesus to the gentiles. Josephus tells us that Paul had 30 days to do offer such a sacrifice from the time he cut his hair. Notice what Josephus says concerning Bernice, the daughter of King Agrippa (Herod of Acts 12):
Now she dwelt then at Jerusalem, in order to perform a vow which she had made to God; for it is usual with those that had been either afflicted with a distemper, or with any other distresses, to make vows; and for thirty days before they are to offer their sacrifices, to abstain from wine, and to shave their heads. [Josephus: Wars of the Jews, 2.15.1]
The shaving of the head was done at the completion of the vow, but the hair grew during the whole time of one’s sanctification to the Lord. Once the head was shaved, one had thirty days to offer up the appropriate sacrifice. Therefore, Paul’s shaving his head in Cenchrea was a public statement to his Jewish brethren that what he had preached to them, concerning Jesus was true, but they had rejected his testimony. Now he would leave them to their decision and fulfill his vow at Jerusalem as the Law of Moses commanded.