The sin of envy

We fight one another, and envy arms us against one another. ... If everyone strives to unsettle the Body of Christ, where shall we end up? We are engaged in making Christ's Body a corpse. ... We declare ourselves members of one and the same organism, yet we devour one another like beasts 

St. John Chrysostom, Hom. in 2 Cor. 27,3-4:PG 61,588

I was looking through contemporary sermons (mostly audio which is difficult) on Sermon Cloud, http://www.sermoncloud.com/, but since the early church struggled with it from the beginning, I think this was one of the best.  “arms us against one another. . .making Christ’s body a corpse.”

St. John Chrysostom was a "golden-voiced" orator and one of the 8 great Doctors of the Church (Ambrose, Jerome, Augustine, Gregory the Great, Athanasius, John Chrysostom, Basil the Great, and Gregory of Nazianzus).