וְכָכָה֮ תֹּאכְל֣וּ אֹתוֹ֒ מָתְנֵיכֶ֣ם חֲגֻרִ֔ים נַֽעֲלֵיכֶם֙ בְּרַגְלֵיכֶ֔ם וּמַקֶּלְכֶ֖ם בְּיֶדְכֶ֑ם וַאֲכַלְתֶּ֤ם אֹתוֹ֙ בְּחִפָּז֔וֹן פֶּ֥סַח ה֖וּא לַיהוָֽה׃
And thus shall ye eat it: with your loins girded, your shoes on your feet, and your staff in your hand; and ye shall eat it in haste—it is the LORD’s passover.
Rashi on Exodus
מתניכם חגרים YOUR LOINS GIRDED — i. e. prepared for the journey (Mekhilta d'Rabbi Yishmael 12:11).
Sforno on Exodus
מתניכם חגורים, ready to commence marching. We find a similar expression in connection with the prophet Elijah in Kings I 18,46 where he is described as וישנס מתניו, “he bound up his loins.” The expression reflects absolute confidence in G’d’s assistance of the undertaking one is about to embark on. This is displayed while the prisoner is still inside the walls of his jail, the door not having opened yet to let him out.
Rashbam on Exodus
פסח הוא לה', to insure that G’d’s angel killing the firstborn will bypass the houses with the sign of the blood on their door-frames.