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 suckers 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 [Joh 19:29].
      none . . . shall go out at the door of his house until the morning--This regulation was peculiar to the first celebration, and intended, as some think, to prevent any suspicion attaching to them of being agents in the impending destruction of the Egyptians; there is an allusion to it (Isa 26:20).

JFB.