Charles Ellicott Commentary Acts 21:20

"And they, when they heard it, glorified God; and they said unto him, Thou seest, brother, how many thousands there are among the Jews of them that have believed; and they are all zealous for the law:" — Acts 21:20 (ASV)

They glorified the Lord.—The better manuscripts state, “they glorified God.” The tense implies continued action, and although its meaning would be satisfied by assuming mere exclamations of wonder and praise, it is, at least, not improbable that there was a more formal thanksgiving.

How many thousands of Jews there are which believe.—Literally, how many myriads—that is, tens of thousands. The numbers seem large if we think of the population of Jerusalem only, but the crowds that came from all quarters to the Feast of Pentecost (see Note on Acts 2:1) would fully justify the statement. The speaker here is obviously Saint James, as the president of the assembly. There is no trace of the presence of any of the Apostles.

They are all zealous of the law.—Better, the word being a substantive and not an adjective, zealots for the law. The term was an almost technical one for the most rigid class of Pharisees. (See Note on Simon the Canaanite, Matthew 10:4.) So Saint Paul describes himself as in this sense a “zealot” (Acts 22:3; Galatians 1:14).