As defined by whom?
Take your time on researching that -- after all, you've got to sift through literally thousands of doctrines and denominations, all of which claim to represent the True Church.
Which one is the right one?
No sifting necessary.
The church is defined by scripture, not by babbelers, nor nicolaitans.
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after all, you’ve got to sift through literally thousands of doctrines and denominations, all of which claim to represent the True Church.
- - — -
Very few protestant denominations claim to be the ‘only true church’.
However, the Restorationist groups (SDA, CoC, LDS, JW, DoC) always claim that and always contain similar heretical teachings (probably because they are all founded upon idea of Alexander Campbell). They are often classified as ‘cults’ of Christianity rather than Christian churches.
There is no ‘right church’ (as in denomination). The word in Greek means ‘assembly’ or those who are called out’. The Church of Christ is the Body of ALL believers in His Grace by way of His death, regardless of where they attend on Sunday.