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.
Related Commentaries of Exodus 12:13
Exodus 12:13
13 And the blood shall be to you for a token upon the houses where ye are: and when I see the blood, I will pass over you, and the plague shall not be upon you to destroyd you, when I smite the land of Egypt.