Hebrews 12:21 - Coke's Commentary on the Holy Bible

And so terrible was the sight, &c.— "The appearance was so dreadful that Moses himself,who was happy in such unparalleled degrees of the divine favour, and accustomed to converse with God in so intimate a manner, when urged by the people to act as their mediator in this awful transaction, said, though I consent to undertake the charge, I do nevertheless exceedingly fear and tremble." This circumstance is not recorded in the Mosaic history; but most probably it was well known to the Hebrews by the means of tradition: for they had so great a veneration for the character and honour of Moses, that they would have been vehemently enraged with the apostle, if they had not themselves been conscious of the truth of the apostle's assertion.