Rich Vincent at TheoCenTric writes:
What does one get when one channels medieval Catholic spirituality through the lens of Protestant theology? The answer: Johann Arndt's spiritual classic True Christianity (1605). Labeled by Albert Schweitzer as "the prophet of interior Protestantism," Johann Arndt presents a mystical theology that is thoroughly rooted in the soil of Lutheran doctrinal distinctives. Consequently, his work provides a good starting point for wrestling with a mystical spirituality that is grounded in Protestant theology.
For more read Protestant Mysticism