That's a big request. UCG isn't a monolithic organization. It's a group of people who believe in certain basic beliefs. Within those beliefs there are variations and shadows.
I would recommend starting at the www.ucg.org perhaps starting at fundamental beliefs.
A general belief, evident from reading the booklet that this article introduces, is that there is a LOT of false religion in the world including within Christianity itself. This should be evident considering especially the corruption of many "main stream" protestant denominations.
However within those organizations it's always considered that there are members of the church of God or at least potential members of the church of God.
I hope that helps/answers your question...
Thanks Doug.
From your link, the UCG does not teach trinitarian doctrine, but something different concerning God the Father, Christ and the Holy Spirit.
As for importance, I can only apply what it says about all its fundamental beliefs including this one:
“We consider the teaching of these beliefs to be critical to building on the right foundation of a proper reverence for God’s Word, especially as revealed in Jesus Christ.”
I would have to assume that those not teaching this belief would lack the right foundation, etc. and therefore be quite unlikely to be among the “Church Jesus Built” per the UCG.
This would exclude pretty much all protestant Christians such as Lutherans, Methodists, Baptists, Presbyterians, etc. and of course Catholics.
Let me know if you think I’m in error here. thanks again...