John Calvin Commentary Acts 21:28

"crying out, Men of Israel, help: This is the man that teacheth all men everywhere against the people, and the law, and this place; and moreover he brought Greeks also into the temple, and hath defiled this holy place." — Acts 21:28 (ASV)

Men of Israel, help. They cry out as if they were in extreme danger, and they call upon all people to help them, as if all religion were at risk. From this we see with what furious hatred they were inflamed against Paul, only because in showing that the full and perfect truth is found in Christ, he taught that the figures of the law had an end.

Now, since they form a false opinion after seeing Trophimus, they betray all the more by this rashness how venomous they are. They accuse Paul of sacrilege. Why? Because he brought into the temple a man who was uncircumcised. But they charged an innocent person with a most cruel crime based on a false opinion.

Thus, the boldness of those who are carried away by a preconceived opinion is often absurd. But let us learn from such examples to beware of disordered passions, and not to allow slight prejudices to take control, lest we rush headlong against the innocent, being carried by blind force.