And you 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 at the door of his house until the morning.
All Commentaries on Exodus 12:22 Go To Exodus 12
Augustine of Hippo
AD 430
They are to bear in mind that those who celebrated the Passover at the time through figures and shadows, when they were commanded to mark their doorpost with the blood of the lamb, marked them with hyssop. This is a mild and humble plant, but it has very strong and penetrating roots. So, “being rooted and grounded in love,” we may be able “to comprehend with all the saints what is the breadth and length and height and depth,” that is, the cross of the Lord. .