[closetkantian]

The Bible, specifically the New Testament, and more specifically，The Gospels. The reason that it's radical is that Christ overturns traditional notions of morality. Greco-Roman thought saw the rich and powerful as close to the divine but Christ's message is that the meek and poor are prefered by God.

Coming in at #2, I would argue for Marx, maybe Capital. It's radical because it shows that Capitalism is not a "natural" state of affairs (as much as it would like us to believe that it is).

[p0d]

Agreed. I love the Old Testament too, as it is so raw and real. Murder, betrayal, sex, prostitution, and war. Interwoven with the hope of a new start with Christ coming to earth, and a new beginning when he returns.