let's break this down, point by point.  1. Your third sentence is your best and most accurate.  2. Your fourth sentence is about as good as the third.  What you fail to mention is the consistency of their words.  The redemption of mankind through Jesus work on the Cross is consistent through the New Testament and even through the Old Testament.  3. God does work through open people, but not just any open people.  Which leads to #4, God didn't work through Buddha, Mohammed, Confucius (the real Confucius, not the Westernized and condensed Confucius), and the writers of the Bhagavad Gita if they weren't in right relationship with God.  They were all men who wrote inspiring things.  But unless those things lead people to a right relationship with the God of Abraham, Isaac and Jacob, the same God who became flesh and dwelt among us and died on the Cross, as described in Psalm 22 and Isaiah 53, then they are just writing inspiring words.  As for God being narrow-minded, that's tween U N Him.