Exodus 12:21-25

Then Moses called for all the elders of Israel, and said unto them, Draw out and take you a lamb according to your families, and kill the passover.

Then Moses called ... Here are given special directions for the observance. The objection recently urged against the possibility of these instructions being conveyed to the whole multitude of Israel in the course of 12 hours is altogether groundless. These directions were not issued so late as the 14th day, because the lamb was to be selected on the 10th day. The directions were given earlier even than that day, so that there must have been plenty of time for the elders to communicate the commands received to their respective tribes.

Verse 22. Hyssop - a small red moss (Hasselquist); the caper plant (Royle). It was used in the sprinkling, being well adapted for such purposes, as it grows in bushes, putting out plenty of tendrils from a single root. And it is remarkable that it was ordained in the arrangements of an all-wise Providence that the Roman soldiers should, undesignedly on their part, make use of this symbolical plant to Christ, when, as our Passover, he was sacrificed for us.

None ... shall go out ... This regulation was peculiar to the first celebration, and intended, as some think, to prevent any suspicion attaching to Hebrews of being agents in the impending destruction of the Egyptians; there is an allusion to it, Isaiah 26:20.

Verse 25. When ye be come to the land ... ye shall keep this service. The ordinance of the Passover was instituted from the beginning with a prospective reference to its annual observance in the promised land.