God walked away. During the Crusades, He just up and left Creation. No warning, no explanation.
In order to avoid a potential invasion from Hell, the archangel Michael, now regent of Heaven, offered an armistice to the Devil. They call this the Covenant. The Lord of Hell only agreed because it gave him time to search for a decisive way to win the eternal conflict, one that would cripple the Host beyond repair.
The Covenant mandates Heaven and Hell keep their hands off of humanity. Both sides must work through proxies, willing mortal souls who became incarnations of the seven heavenly virtues and the seven deadly sins. Thus began the Long Game, a cold war between Heaven and Hell, with plenty of hot incidents along the way.
From Scratch is a fully sketched out setting in the form of a detailed theme document, with all of the world set-up choices written out in detail. The frame is customizable by your game group. You choose a tone, and pick the magic level that is appropriate for your game.
Campaign frames are great ways to do a quick setup for Mortal Coil, and are ideal for playing a pick-up game or convention game. If your players really like the setting, the frame can be used for a longer term game as well. A campaign frame is also useful as a how-to on setting up a unique theme document of your own.