Why Does It Matter Which Higher Power Someone Believes In?

Questions about what to say to a Christian who doesn’t think it matters which higher power a person believes in, how to help friends see they’re attending an unhelpful or heretical church, whether it’s wrong to wish a dead loved one happy birthday, and when to leave a parachurch organization over theological differences.

• What should I say to a “lukewarm” Christian who says people need to believe in a higher power “even if it’s Buddha or something”?
• How do I help a Christian friend see that the church she’s attending is actually hindering her rather than helping?
• What would be a tactical approach to helping friends and family members realize they’re attending a church of a false teacher/heretic?
• Are Christians crossing a line into talking to the dead when they wish a happy heavenly birthday to their dead loved ones?
• How do I know when it’s time to leave a parachurch organization with which I disagree theologically?