John Chrysostom
But tell me, why was the book of the covenant sprinkled? "For when Moses had spoken every commandment according to the law before all the people, he took the blood of calves and goats, with water and scarlet wool and hyssop. And sprinkled both the book itself and all the people, saying: This is the blood of the covenant which God commanded for you." Tell me, then, why are the book of the covenant and the people sprinkled? Because that blood and all the rest were a type of the most precious blood, which was prefigured from of old. Why with hyssop? Because, being dense and soft, it held the blood. Why water? It was used as a sign of cleansing by water. And why wool? It too was used to hold the blood. The Apostle shows that blood and water were here together, because baptism is an image of Christ's Passion.