Theologia Germanica is a very old book that was written a long, long time ago (around 1350!). It is a book that talks about God and religion, and it is written in a way that is easy to understand.
The main idea of this book is that people should focus on their relationship with God more than anything else. The book also talks about how people should live their lives in a way that is good and kind to others.
The book says that God is always with us, watching over us and helping us. It also talks about how we should try to be like God in the way we treat others.
Overall, Theologia Germanica is a book that teaches us about God and how we should live our lives to be close to Him. It is written in a simple way so that even young children can understand it.