TSK · Acts 21:26

take them and purify yourself along with them and pay their expenses, so that they may have their heads shaved. Then everyone will know there is nothing in what they have been told about you, but that you yourself live in conformity with the law.

To the Jews I became like a Jew to gain the Jews. To those under the law I became like one under the law(though I myself am not under the law) to gain those under the law.