When you cast a spell from exile, that counts as casting it
Thats the short version of why this enchantment sees so much play in EDH decks, above all those focusing on typal synergies
Not only do you draw a card, but you can immediately cast a spell from your hand with mana value equal to or less than the damage dealt, without paying its cost
the 10 Ravnica signets with: Reliquary Tower, Reflecting Pool, Path of Ancestry, The World Tree, Second City, Exotic Orchard, Reflective Gate, Commander's Sphere, Vexing Puzzlebox, and Guided Passage
Its a heavily-played card in formats where its legal, and thats mostly Vintage, Legacy, Cube, and EDH, where its a Game Changer