I recently heard a good explanation of having unity of faith with other Believers. The idea was to differentiate non-negotiable and non-essential in viewing doctrines.
A non-negotiable would be God is the creator of all the universe. A non-essential would be where people land on the whole Armenianism and Calvinism spectrum of the free will vs predestination argument.
For example I can be leaning towards the whole Armenian view and still have fellowship with someone who is more leaning toward a Calvinistic ideology. We still agree on the non-negotiable that God is the creator of all the universe so we are united in the same faith.
(Not saying I lean either way for reference this is just an example).
What else can we agree upon to be non-negotiable to the Christian faith? What can we agree are non-essentials?
God bless,
GE