Leviticus 15

The washing which is common to all persons is that of the baths, which usually cleanses away the filth of the body. There is also the washing of the Jews, which is more solemn than that of the baths but much inferior to the bath of grace. While this [baptismal] bath cleanses bodily filth, it does not merely remove the uncleanness of the body but also that which clings to a weak conscience.

For from the beginning "the spirit of God moved over the waters," and over and again Scripture testifies to the fact that water is purifying. It was with water that God washed away the sin of the world in the time of Noah. It was with water that every one who was unclean was purified in accordance with the law, and even their garments were washed with water.

In the past, a man coming from marital intercourse was required to wash. It cannot be too strongly said that the providence of God revealed through the Lord no longer makes this demand. The Lord eliminates washing after intercourse as unnecessary since he has cleansed believers by one single baptism for every such encounter, just as he takes in the many washings prescribed by Moses by one single baptism.