Adam Clarke on Acts 18:13

Persuaded men to worship God contrary to the law - This accusation was very insidious. The Jews had permission by the Romans to worship their own God in their own way: this the laws allowed. The Roman worship was also established by the law. The Jews probably intended to accuse Paul of acting contrary to both laws. "He is not a Jew, for he does not admit of circumcision; he is not a Gentile, for he preaches against the worship of the gods. He is setting up a worship of his own, in opposition to all laws, and persuading many people to join with him: he is therefore a most dangerous man, and should be put to death."