and be ready for the third day. For on the third day the LORD will come down on Mount Sinai in the sight of all the people.
Here, I. God intimates to Moses his purpose of coming down upon mount Sinai, in some visible appearance of his glory, in a thick cloud (Exo 19:9); for he said that he would dwell in the thick darkness (Ch2 6:1), and make this his pavilion (Psa 18:11), holding back the face of his throne when he set it upon mount Sinai, and spreading a cloud upon it, Job 26:9.
Commenting on Exodus 19:9-15
And be ready against the third day,.... Not the third day of the month, but the third day from hence, this being the fourth, and the morrow the fifth, and the third day, the day following that, the sixth, on which day it is generally agreed by the Jews that the law was given; see Gill on Exo 19:16.
Exo 19:10-15 God then commanded Moses to prepare the people for His appearing or speaking to them: (1) by their sanctification, through the washing of the body and clothes (see Gen 35:2), and abstinence from conjugal intercourse (Exo 19:15) on account of the defilement connected therewith (Lev 15:18); and (2) by setting bounds round the people, that they might not ascend or touch the mountain.
Commenting on Exodus 19:10-15