Gregory the Great
Catena Aurea · Matthäusevangelium 11
Then began he to upbraid the cities wherein most of his mighty works were done, because they repented not: Woe unto thee, Chorazin! woe unto thee, Bethsaida! for if the mighty works, which were done in you, had been done in Tyre and Sidon, they would have repented long ago in sackcloth and ashes. But I say unto you, It shall be more tolerable for Tyre and Sidon at the day of judgment, than for you. And thou, Capernaum, which art exalted unto heaven, shalt be brought down to hell: for if the mighty works, which have been done in thee, had been done in Sodom, it would have remained until this day. But I say unto you, That it shall be more tolerable for the land of Sodom in the day of judgment, than for thee.
(Mor. xxxv. 6.) In sackcloth is the roughness which denotes the pricking of the conscience for sin, ashes denote the dust of the dead; and both are wont to be employed in penitence, that the pricking of the sackcloth may remind us of our sins, and the dust of the ash may cause us to reflect what we have become by judgment.