I don’t know if I’d call it “easy” reading, but this is a well-regarded college textbook that’s popular in “Christianity 101” religion classes (so at least it’s entry-level and doesn’t assume prior knowledge on the topic):

bartehrman.com/the-new-testament-a-historical-int…

For something much lighter, Extra Credits did a video series on early Christian schisms that mentions the circumcision debate:

youtube.com/watch?v=E1ZZeCDGHJE&list=PLhyKYa0YJ_5…

I’m far from a religious scholar (just someone who enjoys history from time to time), so I’d be curious if other folks have additional recommendations.