Though many denominations are failing, they will continue to be with us for quite some time.
It will be helpful in your discussions with those stuck in denominational Christianity to understand their history and beliefs.
With the internet you can easily find the denominational website and read their Statements of Faith.
Google searches can give you simple comparisons such as these charts.
A decent printed authority is Frank Mead’s classic, Handbook of Denominations in the United States.
Another decent history of the evolution of denominations in America is Rodney Stark’s Churching of America.
Most people do not understand where the church on the corner came from. They think they are all the same.
Know your history. Know the difference. Know your Bible.
For His glory,
Justin “historian” Johnson