Albert Barnes Commentary Exodus 12:22

"And ye shall take a bunch of hyssop, and dip it in the blood that is in the basin, and strike the lintel and the two side-posts with the blood that is in the basin; and none of you shall go out of the door of his house until the morning." — Exodus 12:22 (ASV)

A bunch of hyssop - The species here designated does not appear to be the plant now bearing the name. It would seem to have been an aromatic plant, common in Palestine and near Mount Sinai, with a long straight stalk and leaves well adapted for the purpose of sprinkling.

Basin - The rendering rests on good authority and gives a good sense; but the word means “threshold” in some other passages and in Egyptian, and is taken here in that sense by some versions. If that rendering be correct it would imply that the lamb was slain on the threshold.

None ... shall go out ... - There would be no safety outside the precincts protected by the blood of the lamb; a symbolism explained by the margin reference.