This is the debate on 'necessity'/'required' from the Lutheran Reformation's perspective, the Reformed have a little different take.
This read is a bit obtuse for our modern standards as well, but interesting.
The Solid Declaration of the Formula of Concord - Book of Concord
This read is a bit obtuse for our modern standards as well, but interesting.
The Solid Declaration of the Formula of Concord - Book of Concord