Let’s do a little Catholicism 101:
Human beings are called, as the first demand of justice, to render unto God that which He is due; namely, to worship Him, not just in the manner of our choosing, but in truth as He Himself has revealed.
So far so good?
Now, there is but one way that fits this description, obviously, and that is through, with and in Jesus Christ and His holy Catholic Church. That is why the popes of tradition didn’t hesitate to speak of the Catholic Church as the one true faith, with all others necessary being in varying degrees, false.
So, what exactly gives rise to the false religions, the adherents of which, in spite of whatever good intentions they may have, do not worship God as justice demands?
The answer is simple, sin, apart from which there would be no such thing as “diversity of religion;” with all of their multiple creeds and conflicting doctrines.
This being the case, can a reasonably well-formed Catholic say that religious diversity among men, such that some are Christian, others Muslim, still others Hindu, and on, and on, and on, is something to be celebrated as a gift?
No, of course not, it is to be lamented, and should lend urgency to our mission to convert the world to Christ and His Church!
Diversity of religion simply means that there are human beings who, wounded by sin, are not worshiping God in the manner that He is due simply by virtue of who He is; in other words, this diversity of religion is about as far from a “gift” as you can get.
Seems simple enough, right?