They shall take of the blood. The blood, which, according to Hebrew ideas, "is the life," and so the very essence of the sacrifice, was always regarded as the special symbol of that expiation and atonement, with a view to which sacrifice was instituted.
As by the Paschal sacrifice atonement was made for the house, which was therefore to escape unscathed, the sign of atonement was to be conspicuously placed upon it. And strike. The "striking" was to be by means of a bunch of hyssop dipped in the blood (Exodus 12:22).
The selection of the doorway as the part of the house to receive the stains of blood is probably to be connected with the idea that the secondary agency producing death, whatever it was, would enter by the door—and if the door showed the house to have been atoned for, would not enter.
The upper door-past. The word used is elsewhere translated "lintel" (Exodus 12:22, Exodus 12:23); but it seems properly to mean the latticed window which was commonly placed over a doorway in Egyptian houses, and which is often represented in the facades of tombs.
It is derived from a root signifying "to look out."