Charge the people lest they break through—i.e; "lest they force a passage through the barrier made by Moses" in accordance with the command given in Exodus 19:12. And many of them perish. Irreverent gazing on holy things was forbidden by the law (Numbers 4:20), and on one occasion (1 Samuel 6:19) was actually punished with death.
It did not, however, require a law to make it an offence, natural reason being quite sufficient to teach the duty of reverence.