Albert Barnes 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. They gave praise to the Lord for what he had done. They saw new proofs of his goodness and mercy, and they rendered him thanks for all that had been accomplished. There was no jealousy that it had been done by the instrumentality of Paul. True piety will rejoice in the spread of the gospel, and in the conversion of sinners, by whatever instrumentality it may be effected.

You see, brother. The language of tenderness in this address, recognizing Paul as a fellow-laborer and fellow Christian, implies a wish that Paul would do all that could be done to avoid giving offense, and to conciliate the favor of his countrymen.

How many thousands. The number of converts at this time must have been very great. Twenty-five years before this, three thousand had been converted at one time (Acts 2), and afterwards the number had swelled to some more thousands (Acts 4:4). The assertion that there were then "many thousands" implies that the work, so notably begun on the day of Pentecost in Jerusalem, had not ceased, and that many more had been converted to the Christian faith.

Which believe. Who are Christians. They are spoken of as believers, or as having faith in Christ, in contrast to those who rejected him, and whose characteristic trait it was that they were unbelievers.

And they are all zealous of the law. They still observe the law of Moses. The reference here is to the law respecting circumcision, sacrifices, distinctions of foods and days, festivals, etc. It may seem remarkable that they should still continue to observe those rites, since it was the manifest design of Christianity to abolish them. But we are to remember,

1. that those rites had been appointed by God, and that they were trained to their observance.
2. That the apostles conformed to them while they remained in Jerusalem, and did not deem it best to set themselves violently against them (Acts 3:1; Luke 24:53).
3. That the question about their observance had never been agitated at Jerusalem. It was only among the Gentile converts that the question had arisen, and there it must arise, for if they were to be observed, they must have been imposed upon them by authority.
4. The decision of the council (Acts 15) related only to the Gentile converts. It did not touch the question, whether those rites were to be observed by the Jewish converts.
5. It was to be presumed, that as the Christian religion became better understood — that as its large, free, and catholic nature became more and more developed — the peculiar institutions of Moses would be laid aside as a matter of course, without agitation and without tumult. Had the question been agitated at Jerusalem, it would have excited tenfold opposition to Christianity, and would have torn the Christian church into factions, and greatly retarded the advance of the Christian doctrine. We are to remember also,
6. that, in the arrangement of Divine Providence, the time was drawing near which was to destroy the temple, the city, and the nation; which was to put an end to sacrifices, and effectually to close for ever the observance of the Mosaic rites. As this destruction was so near, and as it would be so effectual an argument against the observance of the Mosaic rites, the Great Head of the church did not suffer the question of their obligation to be needlessly agitated among the disciples at Jerusalem.