Theologia Germanica
This short, anonymous work is thought to have been written in the 1300s by a member of the lay-religious group called ‘The Friends of God.’ Its central teaching is that humans can become one with God by living a holy, selfless life in which our will is subsumed into God’s, of which Christ is the ultimate example. Martin Luther discovered, named, and published Theologia Germanica in 1516, declaring that, "Next to the Bible and St. Augustine, no book has ever come into my hands from which I have learnt more of God and Christ, and man and all things that are." (Summary by Pleonic)