Jamieson, Fausset and Brown on Exodus 12:11

Ex 12:11-14. The Rite of the Passover.

11. thus shall ye eat it; with your loins girded, your shoes on your feet--as prepared for a journey. The first was done by the skirts of the loose outer cloth being drawn up and fastened in the girdle, so as to leave the leg and knee free for motion. As to the other, the Orientals never wear shoes indoors, and the ancient Egyptians, as appears from the monuments, did not usually wear either shoes or sandals. These injunctions seem to have applied chiefly to the first celebration of the rite.

it is the Lord's passover--called by this name from the blood-marked dwellings of the Israelites being passed over figuratively by the destroying angel.