Bede the Venerable — as excerpted in the Catena Aurea on Mark 9:43-50

“(ubi sup.) We may also understand the altar to be the heart of the elect, and the victims and sacrifices to be offered on the altar are good works. But in all sacrifices salt ought to be offered, for that is not a good work which is not purged by the salt of wisdom from all corruption of vain glory, and other evil and superfluous thoughts.”