Acts 21:26

Verse 26. Then Paul took the men. Took them to himself; united with them in observing the ceremonies connected with their vow. To transactions like this he refers in 1 Co 9:20, "And unto the Jews I became as a Jew, that I might gain the Jews; to them that are under the law, as under under the law." Thus, it has always been found necessary in propagating the gospel among the heathen, not to offend them needlessly, but to conform to their innocent customs in regard to dress, language, modes of travelling, sitting, eating, etc. Paul did nothing more than this. He violated none of the dictates of honesty and truth. Purifying himself with them.