Sanctify yourselves against tomorrow. By certain ablutions, and by avoidance of legal pollution (see Exodus 19:10, Exodus 19:14, Exodus 19:15). The people were to prepare themselves as for some revelation of God's holiness and majesty.
In truth it was for a revelation of his wrath, and of the bitter consequences of sin. There is about the words, as interpreted by the result, a depth of very terrible meaning; it was as though a traitor, unknowing of his doom, were bidden to a grand ceremonial on the morrow, which ceremonial should be his own execution.
For it was well with us in Egypt. These false and wicked words, in which the base ingratitude of the people reached its highest pitch, are repeated to them in the message of God with a quiet sternness which gave no sign to their callous ears of the wrath they had aroused.