On the contrary, I think God (that’s the one true God, the God of Abraham, Isaac and Jacob) cares quite a bit about how we interpret Scripture [that’s the Old & New Testaments of the Holy Bible, excluding the apocrypha (along with all their false teachings)] that the Catholics accept. The fact that He gave us His Word which is so explicit about what He wants us to believe and how to live and (wholly) sufficient to gain understanding on any subject proves how much He cares.
The Calvinists and the Catholics don’t believe in the correct doctrine of salvation. Both the Catholic and the Calvinist beliefs on the topic are antithetical to what Scripture says and wholly inconsistent with the nature of God presented in Scripture. Their beliefs are founded on twisting of Scripture and uninspired canon. If you don’t even have the doctrine of salvation, which is the entry point to the Christian faith, correct then how do you proceed any further? At the time Martin Luther enlightened many (freeing them from the corrupted Catholic Church), John Calvin came to mislead many.
Jesus Christ (the Christ of the Scriptures) is the only way to God. The Jews have largely rejected Him. That said there are many who have been, are being and will be saved. For God’s chosen people His promises will be kept.
As for Islam, Mormonism, Jehovah’s Witnesses and all the other false religions of the world see the first sentence of my previous paragraph. There is no hope in any other and no other source for salvation.
On the subject of the many denominations of Christianity, some schisms initially occurred over secondary issues but it looks like many are now truly disqualifying themselves as they increasingly adopt false teachings.
True Christianity is by nature narrow and exclusionary (necessarily so and according to Scripture). Many will see those as negative connotations but they are not and I would simply tell them to study and decide for themselves whether my claims are true or not.