Were I still a Christian I might respond to that with the parable of a rich man who threw a party and invited the best folks in town. But they turned him down. Eventually he invites in the rabble and a good time was had by all. Except some dude who didn't put on his Sunday best. They threw him out.
If memory serves growth in Christianity is mostly in Africa now. As one African put it "when the missionaries came we had the land and they had the Bibles. Now we have the bibles and they have the land."
There has always been churn across religions. This one repents, that one apostates. This one finds Allah, That one finds Jesus, another sits in the quiet seeking to extinguish desire, while his negotiations seeks The Way. Sometimes I think the sorting hat did a lousy job and we're all left to find our own house.
What makes it more vital than any other religious book? This sentence could be applied to any of them depending on where you were born.