If this book (or variants) has already been mentioned forgive me. Before I was married under the care of a Meeting (my fiancée was a Quaker at the time), I sought out more on Quakerism, and was given The Book of Discipline.
en.wikipedia.org/wiki/Book_of_Discipline_(Quaker
What I found to be a bit of let down was the lack of liveliness or vitality in the corpus of beliefs. I don’t mean a cheap modernism at all. I mean instead that there was this apparent gap in current practical moral specifics tied back to a core of unchanging beliefs (abortion, remarriage after divorce, sexual matters, details of spiritual formation, catechesis, exegesis).
It seemed to me at least that many of the younger Quakers were quite encouraged to roll their own beliefs, and they weren’t being hesitant.
Instead, if you read John Paul II’s Theology of the Body, one is struck by the “rootedness” and substantialness of his thinking. Nothing will need changing. It’s already reconciled to the base of the Church’s beliefs. It’s current and it’s old.
Just my two cents.