Levítico 1

Levítico 1:14

In very many ceremonies of the law one who needed to be cleansed was ordered to be cleansed by [offering] these [birds]. A pigeon indicates simplicity and a turtledove indicates chastity, for a pigeon is a lover of simplicity and a turtledove is a lover of chastity—so that if by chance one loses its mate it will not subsequently seek another. — Homilies on the Gospels 1.18