22 Take a bunch of hyssop and dip it in the blood that is in the basin, and touch the lintel and the two doorposts with the blood that is in the basin. None of you shall go out of the door of his house until the morning. 23 For the Lord will pass through to strike the Egyptians, and when he sees the blood on the lintel and on the two doorposts, the Lord will pass over the door and will not allow the destroyer to enter your houses to strike you.
Matthew Henry's Commentary on Exodus 12:22-23
Commentary on Exodus 12:21-28
(Read Exodus 12:21-28)
That night, when the first-born were to be destroyed, no Israelite must stir out of doors till called to march out of Egypt. Their safety was owing to the blood of sprinkling. If they put themselves from under the protection of that, it was at their peril. They must stay within, to wait for the salvation of the Lord; it is good to do so. In after-times they should carefully teach their children the meaning of this service. It is good for children to ask about the things of God; they that ask for the way will find it. The keeping of this solemnity every year was, 1. To look backward, that they might remember what great things God had done for them and their fathers. Old mercies, to ourselves, or to our fathers, must not be forgotten, that God may be praised, and our faith in him encouraged. 2. It was designed to look forward, as an earnest of the great sacrifice of the Lamb of God in the fulness of time. Christ our passover was sacrificed for us; his death was our life.