The Last Days of God by James Chrisman

Heaven and Hell are at War, and Heaven is losing. Badly. Their armies are outmatched in every way, their leadership is depressed, drunk, and falling apart, and to top it off the Four Horsemen of the Apocalypse, historically neutral in the conflict, have agreed to assassinate the Archangels.

In a last-ditch attempt to save Heaven from complete collapse and annihilation, God has reached out to Earth, whom he abandoned after its own apocalypse, to collect the Earth's best warriors. These human soldiers will stand as the last bastion against the Horsemen.

For Amedeo and his friends though, none of that matters. They're in it for the fun and the bragging rights of killing someone from the bible. For funsies.