Them take, and purify yourself with them, and pay their expenses, that they may shave their heads: and all may know that those things, of which they were informed concerning you, are nothing; but that you yourself also walk orderly, and keep the law.
Read Chapter 21
George Leo Haydock
AD 1849
Bestow on them. It was thought a merit among the Jews to bear the expenses of any vow which another had made. They thus became partakers of it; in the same manner as at present those, who have not the courage to forsake the world by solemn vows, seek to have some share in the merits of those who do forsake it, by contributing part of their substance to their support. (Calmet)
He shows that it was not necessary to do this upon principle (προηγουμένως)— whence also they obtain his compliance— but that it was economy and condescension. As touching the Gentiles, etc.
they say not, teachest, but, of superabundance, that you yourself also keepest the law. For of course not this was the matter of chief interest, whether he did not teach others, but, that he did himself observe the law. What then (he might say), if the Gentiles should learn it? I shall injure them. How so? Say they, seeing that even we, the teachers of the Jews, have sent unto them. As touching the Gentiles which believe, we have written and concluded that they observe no such thing, save only that they keep themselves from things offered to idols, and from blood, and from strangled, and from fornication.
Keeping the law: The law, though now no longer obligatory, was for a time observed by the Christian Jews: to bury, as it were, the synagogue with honour.