It is Benedict XIV' Constitution, "Etsi Minime".
Is it? As I was looking into it I figured it was his Institutiones Ecclesiasticae
, and probably from volume I, likely chapter 27 (the citation in the enclycical indicates instit.
27:18 ). I'm unsure what the "18" refers to. This copy (the only complete copy I could find) does not have numerated subdivisions within each chapter: https://books.google.com/books?id=QHWmru22PGoC&printsec=frontcover#v=onepage&q&f=false
I tried to locate Pius X's citation but I couldn't. I'm not much of a Latinist, though, I'm sure someone else could.
Mmmm, so Christians are bound to the knowledge of specific truths of salvation but non-Christians can get away with not knowing?
It would seem than the knowledge of Christ and His Church (with the strict obligations that come with it) is rather a curse, then.
I don't see how that follows from the quote you provided. I was responding to your question
viz. "what mysteries is Pope Pius X" referring to? He doesn't, after all, say
. He cites another pope (incidentally, Institutiones Ecclesiasticae
was a compilation of Benedict XIV's legal and pastoral works written before he was pope, published after he was pope. At least, that's what I've gathered from looking into it. Makes for an interesting case study in determining what magisterium it belongs to).