Maybe the Belloc piece was less accessible than I thought, but then I read a lot of old things, and I've read a lot of him and his contemporaries. I remember that GK Chesterton took me some getting used to until someone explained to me how he operated, and then he became one of my favorite authors.
Anyway, I thought the main thrust of the article was that in dealing with people who are good at rational thinking but don't yet have faith, it is helpful to be aware that some of the truths of the Catholic Faith are accessible to human reason without the help of revelation, while others - the mysteries of faith, while just as true, are not.
This is what I thought the main things to take away from the piece were:
1.) You can't go around getting all offended that people who aren't Catholic don't believe the articles of faith. This is not only silly and illogical, but scandalous and harmful to evangelization: if you go around acting like any reasonable person should be able to arrive at the mysteries of faith, all you do is convince rational people that the Catholic Church is silly and illogical, just another lazy man's substitute for clear thinking.
2.) There are a lot of people who are competent rational thinkers, but not having the benefit you have of revelation from God, are basically trying to figure out the nature of the world and human life from scratch. Maybe, since they don't know if you're on the right track and don't know the Church and so can't be expected to accept her authority right off, it would be good with them to start with the truths of religion that can be reached by reason alone (of which there are many). Then when they see how reasonable and truthful the Church is, they can be invited to consider that the Church is right about things that can't be known except by divine revelation, like the Trinity, and the Incarnation, and so forth.
This latter, in essence, was recently proposed to us by Pope Benedict, who suggested that we might start with the content of Natural Law as a basis for dialogue with unbelievers. Except that nobody in the media understands what is meant by the term "Natural Law," since it's an infrequently used term in common speech these days, and since it's the contrary of Relativism (the only mode in which many people in our culture are used to thinking), so this didn't get a lot of reportage.