Isaiah 66:21 - Matthew Poole's English Annotations on the Holy Bible

Lest the Jews, being assured that the tribe of Levi, which God anciently chose to minister before him, was among them, should say, Alas, if the Gentiles should be brought in, where would they have priests or Levites? God here by his prophet tells them he would provide priests, he would take of them, of these converted heathens. for priests and Levites, that is, for gospel ministers, to teach and to instruct people, which was the priest's work of old, Deuteronomy 33:10 2 Chronicles 17:7,9 Mal 2:6; for they are mightily mistaken that think the priests among the Jews had nothing to do but to sacrifice and burn incense, which work is ceased. Saith the prophet, God will find amongst the converted Gentiles those who, though they be not of the tribe of Levi, or house of Aaron, yet they shall do the true work of priests and Levites.