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
Gregory the Theologian
AD 390
Be it so, some will say, in the case of those who ask for baptism; what have you to say about those who are still children and conscious neither of the loss nor of the grace? Are we to baptize them too? Certainly, if any danger presses. For it is better that they should be unconsciously sanctified than that they should depart unsealed and uninitiated. A proof of this is found in the circumcision on the eighth day, which was a sort of typical seal. It was conferred on children before they had use of reason. And so is the anointing of the doorposts, which preserved the firstborn, though applied to things which had no consciousness.