Seeing then - Since no one can call in question the zeal of the Ephesians on this subject, or doubt the sincerity of their belief, and since there can be no danger that this well-established worship is to be destroyed by the efforts of a few evil-disposed Jews, there is no occasion for this tumult.
Be quiet - Be appeased. The same Greek word which is used in Acts . Acts 19:35, "had appeased the people."
To do nothing rashly - To do nothing in a heated, inconsiderate manner. There is no occasion for tumult and riot. The whole difficulty can be settled in perfect consistency with the maintenance of order.

Seeing then that these things cannot be spoken against,.... This officer intimates, in order to quiet the mob, and make them easy, that these things were so certain, and well known, that nobody would pretend to contradict them, and therefore they must be mistaken in the men, whom they had hurried into the theatre; it was impossible that they, or any men, should be capable of saying any thing against the truth of these things: therefore
ye ought to be quiet and do nothing rashly; to these men, to their hurt, but sit down, and compose yourselves, and think again, and consider of this matter, and not go into any hasty measures, which may, in the issue, be prejudicial to yourselves.

Seeing that these things cannot be spoken against, &c.--Like a true legal man, he urges that such was notoriously the constitution and fixed character of the city, with which its very existence was all but bound up. Did they suppose that all this was going to be overturned by a set of itinerant orators? Ridiculous! What did they mean, then, by raising such a stir?