What does Acts 21:17 mean?

Paul must have very mixed feelings. He is glad to be back in Jerusalem. His companions can finally deliver the donations they have collected from their home churches to the apostles who first spread the message of Jesus (Acts 20:4; Romans 15:26). Paul can give the Jerusalem elders an account of the healthy churches in Ephesus, Troas, Philippi, Thessalonica, Berea, and Corinth. Despite various troubles—especially in Corinth—they faithfully follow Christ.

It's unclear who "the brothers" are. They might be Mnason's household (Acts 21:16) or an assortment of Jesus-followers in Jerusalem. Paul will not meet with James and the church elders until the next day, but this gathering may include some of the apostles. Either way, it's a warm welcome after several years apart.

Paul enjoys it while he can. He will soon learn that despite his sacrifices and faithfulness, he is the victim of a rumor. Some claim he has forsaken and rejected entirely the Mosaic law, and encouraged other Jews to, as well. As he goes about proving his respect for Mosaic law, another group of people wrongly accuse him. This time, the claim is that he brought a Gentile into the temple. Mischief ensues, and the Romans place Paul under house arrest for five years.

This day, however, he enjoys the provision of good friends that God provides. As he later writes the Philippians while under house arrest in Rome, "I have learned in whatever situation I am to be content" (Philippians 4:11).