To fast as in Mark 2:19, signifies to mourn on account of the defect of truth and good. Fasting corresponds to temptation.

In 2 Samuel 12:23, this signifies to mourn because of some lack, usually of truth and good. (Apocalypse Explained 1189[2])

In Matthew 4:2; 6:16; Mark 2:19; Luke 4:2; 5:34, this signifies affliction such as occurs in temptations. (Apocalypse Explained 730[41])

In Matthew 9:15, this signifies that they are in an unhappy state when good is no longer conjoined with truths. (Arcana Coelestia 9182[10])

(Odkazy: Apocalypse Explained 1189; Mark 2)