" I don't know German but pretty sure it's religious."
Ohh yes it is! It is what in English is called an Hymn Book (mark on back: Gesang Buch).
The other marking are "God is Love" and "Only God above shall be praised and honored".
From the two names below the hymns it seems to be lutheran.
Such books were often extremly artful and decorated since they were giveaways from people like uncel&aunt, godfather (if lutehrans have ones) on specific rellllllligious occassion (confirmation, first communion).
Greets
Namxat