In what ways can we use Christ as therapy w/ mental issues like anxiety & depression?

If God never changes (& presumably never changes His mind), why pray? And why would Abraham, Moses, etc. need to beg him not to destroy [insert group here]. Is God just using the Socratic Method on us?

Are Protestants part of the Mystical Body of Christ, and if so, can they be fully united to it (or are they always slightly separated, much like a Catholic who needs to go to Confession)?

Is everyone in Heaven Catholic (even if they were, say, atheist or Hindu on earth)? What does it mean to be catholic?

Why do we believe in the Trinity, if it is not found in the Bible?

How does Purgatory work in terms of time? Is it possible to know when a dead loved one is out of Purgatory & in Heaven? (i.e oh, it has been a year, so-and-so must have been purified by now, he was a good person)

If God seeks to draw all people to Himself, why does he grant some people the gift of faith & not others?