{4} And when they heard it, they glorified the Lord, and said unto him, Thou seest, brother, how many thousands of Jews there are which believe; and they are all zealous of the law:

(4) In things indifferent (of which sort the traditions of the Pharisees were not, but rather the ceremonies of the Law, until the time when Christian liberty was more fully revealed to the Jews) charity exhorts us to conform or apply ourselves willingly so far as we may, to our brethren who do not stubbornly and maliciously resist the truth (but are not thoroughly instructed), especially if the question pertains to a whole multitude.

People's New Testament

21:20-22 When they heard it. Paul's report of the wonderful success of the gospel. They evidently approved of and sympathized with his work.

Thou seest, brother, now many thousands... believe. The Greek reads: How many tens thousands. There were not only many thousands of Christians in the Jerusalem church, but many thousands of Jewish Christians who had come up to the feast of Pentecost. Twenty-seven years before there were five thousand men who believed in Jerusalem (Ac 4:4).

They are all zealous for the law. Zealots for the law in the Greek. They believed upon Christ as the Messiah, but did not understand that the Old Covenant had passed away to give place to the New (Heb 8:13). Hence, while they observed the Christian rites, they still kept up the forms of Judaism. It took a direct interposition of the Spirit to teach that Gentiles were entitled to baptism without circumcision (Ac 10:46-48). It required a council in Jerusalem to settle the question that Gentile Christians were not to keep the Jewish law (Ac 15:19-21). God taught the church, lesson by lesson, but up to this time that at Jerusalem had not yet learned that they were freed from the obligation to keep the law of Moses.

Wesley's Notes

21:20 They are all zealous for the law - For the whole Mosaic dispensation. How astonishing is this! Did none of the apostles, beside St. Paul, know that this dispensation was now abolished? And if they did both know and testify this, how came their hearers not to believe them?

Jamieson-Fausset-Brown Bible Commentary

20-25. they glorified the Lord, &c.-constrained to justify his course, notwithstanding the Jewish complexion of the Christianity of Jerusalem.

Matthew Henry's Concise Commentary

21:19-26 Paul ascribed all his success to God, and to God they gave the praise. God had honoured him more than any of the apostles, yet they did not envy him; but on the contrary, glorified the Lord. They could not do more to encourage Paul to go on cheerfully in his work. James and the elders of the church at Jerusalem, asked Paul to gratify the believing Jews, by some compliance with the ceremonial law. They thought it was prudent in him to conform thus far. It was great weakness to be so fond of the shadows, when the substance was come. The religion Paul preached, tended not to destroy the law, but to fulfil it. He preached Christ, the end of the law for righteousness, and repentance and faith, in which we are to make great use of the law. The weakness and evil of the human heart strongly appear, when we consider how many, even of the disciples of Christ, had not due regard to the most eminent minister that even lived. Not the excellence of his character, nor the success with which God blessed his labours, could gain their esteem and affection, seeing that he did not render the same respect as themselves to mere ceremonial observances. How watchful should we be against prejudices! The apostles were not free from blame in all they did; and it would be hard to defend Paul from the charge of giving way too much in this matter. It is vain to attempt to court the favour of zealots, or bigots to a party. This compliance of Paul did not answer, for the very thing by which he hoped to pacify the Jews, provoked them, and brought him into trouble. But the all-wise God overruled both their advice and Paul's compliance with it, to serve a better purpose than was intended. It was in vain to think of pleasing men who would be pleased with nothing but the rooting out of Christianity. Integrity and uprightness will be more likely to preserve us than insincere compliances. And it should warn us not to press men to doing what is contrary to their own judgment to oblige us.