I used to know an "evangelist" who would close every sermon with the old "God casts a vote, Satan casts a vote, and you cast a vote. Which side are you going to vote for?"
When I was in Seminary I worked for Midwest Federal, downtown. A lot of the guys who worked in the parking garage were students at North Central Bible College (AOG/Pentecostal). We would get talking and I would say that salvation is not by works and they, inevitably would respond, "Well, you gotta do something!"
There are many things that differ between the various churches, baptism, polity, autonomy, ordinances verses sacraments, the pastoral office, and those are what so many arguments center around.
But the devil has gone after the most important doctrine of all: The Gospel. And he has so subtly twisted it that many (most) have failed to see his monstrous deception.