So why were b'nei yisrael commanded to eat the korban pesach with matza? The Ralbag has an interesting approach. In Sh'mot 12:11:
יא וְכָכָה, תֹּאכְלוּ אֹתוֹ--מָתְנֵיכֶם חֲגֻרִים, נַעֲלֵיכֶם בְּרַגְלֵיכֶם וּמַקֶּלְכֶם בְּיֶדְכֶם; וַאֲכַלְתֶּם אֹתוֹ בְּחִפָּזוֹן, פֶּסַח הוּא לַָה.In Ralbag's biur of 12:8 and later in the third toelet he suggests that the korban pesach was eaten with matza because of the need for חִפָּזוֹן.
In his biur on 12:11 the Ralbag explains the reason for חִפָּזוֹן.
...they ate it בְּחִפָּזוֹן and quickly in the manner of people who are planning to go on a journey in order to arouse them to the notion that Pharoe would definitely send them out this time - even though his heart had been hardened in all the previous makkot; in this way their belief in Hashem would increase when they would see that what Hashem promised was fulfilled; this is because the entire purpose was to remove them from their false beliefs and to bring them to the true belief - in this manner they would fully attain true human felicity and be fit to inherit the land, as was previously discussed. It is clear that this command was only in regards to the pesach of Mitzrayim.The Ralbag seems to be saying that the reason for the חִפָּזוֹן was to increase the peoples trust in Hashem. This answer seems incomplete. חִפָּזוֹן would certainly explain why they had to have their belts tied and their walking stick in hand etc. but not why they ate it with matza and marror. As the Ralbag himself points out the mitzvot related to חִפָּזוֹן were only for the pesach of Mitzrayim. Why would matza and marror remain for all generation and the other mitzvot fall away if they are all done because of חִפָּזוֹן? I do not think the Ralbag answers this question. Further thought is required.