John Calvin Commentary Acts 19:25

"whom he gathered together, with the workmen of like occupation, and said, Sirs, ye know that by this business we have our wealth." — Acts 19:25 (ASV)

By this craft. Demetrius here shamefully betrays his malice. It is permissible for a person, to some extent, to provide for their private profit; however, to disturb the public peace for one's own gain, to overthrow fairness and justice, to give oneself over to violence and murder, and to deliberately extinguish what is just and right; that is too great a wickedness.

Demetrius confesses that this is the core of the issue, namely, that Paul denies that those are gods which are made with human hands. He does not inquire whether this is true or not; but, blinded by a desire for gain, he is driven headlong to suppress true doctrine.

The same blindness drives him headlong to seek violent solutions. Also, the craftsmen, because they are afraid of poverty and hunger, run headlong just as violently. For the belly is blind and deaf, so that it cannot recognize any fairness. For this reason, each of us ought to be more suspicious of ourselves when the matter concerns our own gain and profit, lest the same greedy desire that drove these men to such madness remove all distinction between justice and injustice, between what is shameful and what is honorable.