From her essay entitled The Other Six Deadly Sins as found in her book Letters to a Diminished Church.
The sixth deadly sin is named by the Church acedia or sloth. In the world sloth calls itself tolerance; but in hell it is called despair. It is the accomplice of every other sin and their worst punishment. It is the sin that believes in nothing, cares for nothing, seeks to know nothing, interferes with nothing, enjoys nothing, loves nothing, hates nothing, finds purpose in nothing, lives for nothing and remains alive only because there is nothing it would die for. We have known it far to well for many years. The only thing perhaps that we have not known about it is that is a mortal sin. (103)
A few paragraphs later Sayers shares an excellent quote about the intellectual life:
Let us take particular notice of the empty brain. Here sloth is in a conspiracy with envy to prevent people from thinking. Sloth persuades us that stupidity is not our sin, but our misfortune; while envy, at the same time, persuades us that intelligence is despicablea dusty, high-brow, and commercially useless thing. (104)
A little earlier in the essay Sayers discusses Envy:
Hand in hand with covetousness goes its close companion-invidia or envy-which hates to see other men happy...At its best envy is a climber and a snob; at its worst, it is a destroyer; rather than have anybody happier than itself,it will see us all miserable together. (99)