In my essay "The Cosmos and the Cause," I told how, when I was in high school, a priest gave my class a methodology for "proving" the truth of Catholicism. Start by assuming nothing; consider first whether a Supreme Being/Creator necessarily exists; and go on from there to consider all the major religions, then denominations within the "correct" religion. At age sixteen, I accepted all his arguments. But in my mid-twenties, I had doubts.
"I decided to use the methodology that priest had suggested. Started from the beginning, and asked whether the existence of the Cosmos is necessarily dependent on the prior existence of an Uncaused Cause - namely, 'God.'
"As an adult, my answer was No.
"So I had no need to go further, and weigh the merits of different religions. (But I have learned a good deal about Christianity, and see no reason for embracing it.)"
It's occurred to me that my family or friends might someday be interested in my understanding of Christianity. Especially since I know much more now than I did when I was a (grudgingly) practicing Catholic!
I've learned it from the books, video courses, and blog of Bart Ehrman, head of the Department of Religious Studies at The University of North Carolina at Chapel Hill. He himself is an agnostic/atheist, but specifically because he can't reconcile the amount of suffering in the world with the existence of an all-powerful, loving God. I'm sure I would have had a problem with that too, if I'd gotten that far in my thinking! We came at it from different directions: he accepting theism as a "given" until he saw reasons to doubt it, I starting without assumptions and not finding it necessary.
I'm amazed now at how little my younger self knew about Christianity. And I suspect that many of today's lay Catholics are just as uninformed. Here, I'll address a number of topics, devoting a chapter to each one. If the number of chapters seems daunting, some of them will be short!