The root of all sin and the first sin is to lust after godhood (the power, fame, knowledge, etc). I see it in myself and in others. Some people do claim to have God in their pocket and have special powers from God. False preachers and prophets have always been around. The Bible warns us about them, from Old to New Testament.
Since God speaks to the hearts of every man, and all men have basically the same nature, no wonder there are similarities among the religions. But there are also vast differences, and core doctrinal incompatibilities. Diversity and unity are both strengths. Even in the churches I've joined, where everyone has the same core beliefs (or claims to) there are big differences. Many don't like my interest in digging deep and being open, even questioning God. Some Christians tell me to simply have faith and shut up. I clearly find the opposite in the Bible. But I also have my supporters. Iron sharpens iron. I am as bias as the next guy, and have been deeply in error in the past. There is a time to question and a time to shelf questions and commit to a faith. Atheists and Skeptics have their own set of doctrines, dogmas, and faiths.
1 Cor 12 tells about the vast diversity of the body (God's people); yet they are united into one cohesive body. This unity that is the foundation of the love chapter 1Cor 13. I can best love (and probably only love) that which I am eternally and deeply connected to.
Preachers often try hard to prevent disagreement; fearing a church split. I experienced one. Very ugly. Cut the budget in half (they sure don't like that, with good reason). Also, the weak-minded want conformity; and difficult verses can cause some to diminish or lose faith. So many preachers seem try too hard to create cookie-cutter, simple-minded, easily-led believers. I oppose that common extreme. The best churches have brave leaders and attract brave believers. If believers are so fragile, they need a painful spiritual crisis, not a protective play-pin. We were not put in this world to hide in holes, singing sappy songs to each other (exaggeration to make a point).