Church legally defined

The Church can only be defined by Christ but a legal definition is available:

CHURCH In its most general sense, the religious society founded and established by Jesus Christ, to receive, preserve, and propagate his doctrines and ordinances.

A body or community of Christians, united under one form of government by the profession of one faith, and the observance of the same rituals and ceremonies.

Black's Law Dictionary 3rd, 4th, 5th, 6th... eds.