Early in the history of the church Theodosius passed a decree that only churches that acknowledged and worshipped the holy Trinity should be called catholic and that those of a different opinion should be called heretics. The church is also called catholic because it extends throughout the whole world. Lastly, it is catholic, because the church will continue through all ages until the end of the world. I don't have a great application for all this. I guess my application is that we should consider carefully how we treat each other.
Truth is objective in nature, but our interpretation of it is far from perfect.
This will go far in advancing and maintaining the unity of the faith.