Exodus 12:13

A token, both to you, as he now said, a sign and a pledge to confirm your faith in the expectation of the promised deliverance; and to the angel, that he may know and pass over your houses, as the following words intimate. See Poole on "Exodus 12:7". This is spoken of God after the manner of men; the sense is, If I find that you keep the condition which I require, you may expect the privilege which I have promised you; otherwise not.