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
Ambrose of Milan
AD 397
For he who is baptized is seen to be purified both according to the law and according to the gospel. According to the law, because Moses sprinkled the blood of the lamb with a bunch of hyssop. According to the gospel, because Christ’s garments were white as snow, when in the gospel he showed forth the glory of his resurrection.