Charles Ellicott 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 “hyssop” (êzob) of the Old Testament is probably the caper plant, now called asaf, or asuf, by the Arabs, which grows plentifully in the Sinaitic region (Stanley: Sinai and Palestine, p. 21) and is well adapted for the purpose spoken of here. It was regarded as having purifying properties (Leviticus 14:4; Leviticus 14:49–52; Numbers 19:6; Psalms 51:7) and was therefore suitable for sprinkling the blood of expiation.

In the bason.—The word translated “bason” also has another meaning, namely, “threshold;” and this meaning was preferred here by both the Septuagint and Jerome. Whichever translation we adopt, there is a difficulty in the occurrence of the article, since neither the threshold nor any bason had been mentioned previously. Perhaps Moses assumed that whenever a victim was offered, the blood had to be caught in a bason, and therefore spoke of “the bason” as something familiar to his hearers in this connection. If the lamb had been sacrificed on the threshold, it would scarcely have been necessary to put the blood on the lintel and doorposts also.

None of you shall go out.—Moses seems to have given this command by his own authority, without any positive Divine direction. He understood that the Atoning blood was the sole protection from the destroying angel, and that outside the portal sprinkled with it was no safety.