The Exodus reading today is about envy directed at Moses. St. Thomas deals with envy in the Summa, q. 36 of part II-II:
"Charity rejoices in our neighbor's good, while envy grieves over it...." Then he lists some of the things that envy brings along:
"tale-bearing, detraction, joy at another's misfortune, grief at another's prosperity" and finally this all leads to hatred.
Envy is one of those sins that few people like to admit to, because it seems like we fall into it because we think we're inferior in some way. St. Thomas' reflections on it make me ask myself today: if I say something negative about someone else, is envy at the root of it?