Hyssop grew commonly on rocks and walls in the Near East and Egypt ( Exodus 12:22). If it was the same plant that we identify as hyssop today, masses of tiny white flowers and a fragrant aroma characterized it. The Jews used it for applying blood to the door in the Passover ritual because of its availability and suitability as a liquid applicator. They also used it in the purification rite for lepers ( Leviticus 14:4; Leviticus 14:6), the purification rite for a plague ( Leviticus 14:49-52), and for the red heifer sacrifice ritual ( Numbers 19:2-6). [source][source][source]
"The hairy surface of its leaves and branches holds liquids well and makes it suitable as a sprinkling device for purification rituals." [1][source]
"The people were instructed that the only way they could avert the "destroyer" was to put the blood of the lamb on their doorposts. Though the text does not explicitly state it, the overall argument of the Pentateuch ... would suggest that their obedience to the word of the Lord in this instance was an evidence of their faith and trust in him [2]." [3][source]
God through Moses stressed the significance and the importance of perpetuating the Passover ( Exodus 12:26). [source][source][source]
"The Israelitish child will not unthinkingly practice a dead worship; he will ask: What does it mean? and the Israelitish father must not suppress the questions of the growing mind, but answer them, and thus begin the spiritualizing [3]4 of the paschal rite." [5][source]
Worship and obedience occur together again here ( Exodus 12:27-28). These are the two proper responses to God"s provision of redemption. They express true faith. These are key words in Exodus. [source][source][source]
"The section closes with one of those rare notices in Israel"s history: they did exactly what the Lord had commanded ( Exodus 12:28)-and well they might after witnessing what had happened to the obstinate king and people of Egypt!" [6][source]
"By this act of obedience and faith, the people of Israel made it manifest that they had put their trust in Jehovah; and thus the act became their redemption." [7][source]