The passage Balthazar is reading is from the introduction to the “Demons” entry of the Dungeons & Dragons Monster Manual. The full paragraph reads:
Spawned in the Infinite Layers of the Abyss, demons are the embodiment of chaos and evil – engines of destruction barely contained in monstrous form. Possessing no compassion, empathy, or mercy, they exist only to destroy. The Abyss creates demons as extensions of itself, spontaneously forming fiends out of filth and carnage.
And this is just not a very nice thing to say, honestly.
I drew this comic to include as the interstitial illustration following the sixth chapter of The Demon King, which I’m posting on AO3 (here).