The Church
nowhere was Lex Orandi est Lex Credandi more obvious than in the doctrine of the Church, the Ekklesia, or assembly (in English the word church comes from Kyrakon, of the lord - KC). Paul refers to the local Church of Corinth but also in Colossians 1.18 to the global church: "Christ is the head of the body, the church"; (the connection between local and global has never been broken in Catholicism - KC). The beginning in the 2nd century of the idea of an impaired church, united in The Spirit but divided in the flesh.
The Gnostic challenge prompted both the concept of heresy and the authority of bishops. Irenaeus (115-202) and Tertullian responded to Marcion's theory of 'secret teaching' with the concept of apostolic succession which began as a doctrinal concept but evolved into the physical heredity of the laying on of hands from the Apostles onward.
By the 3rd Century, most people believed that the holiness of the Church, united in worship, primarily Eucharistic, was impaired by sin but the only damning offences were homicide (which explains Christian problems with imperial military service), fornication and apostasy; but some said that there could be penitence and restoration, even for these.
The major conflict over sin flared up in the Donatist controversy in North Africa over the issue of whether priests who had been apostate during persecution could continue to preside 'effectively' at the Eucharist. Augustine said that there was no salvation outside the Church with its four marks: one, holy catholic and apostolic; he stressed the difference between the perfect invisible and the impaired visible church (subsequently taken up by Protestants - KC); but the two are connected; therefore, the closer union of the two must be affected by penance. Augustine's Neoplatonism pushed the Church to hierarchy, the invisible over visible and through his doctrine of penance, the clergy over the laity.
Post Constantinian worship moved towards elaborate ritual; the clergy performed, the faithful watched. The collapse of the Western Empire and the civic role of bishops (Pope Gregory the Great (r 590-604) was the ruler and administrator of Rome) led to further clericalism. The Medieval Papacy reached its zenith under Innocent III (r 1198-1216), codified in the Fourth Lateran (1215) and survived for a century until the overblown claims of Boniface VIII (r 1294-1303), followed by Schism, self indulgence and decline.
Protestantism followed Augustine in distinguishing between the invisible and visible church to justify its 'churchness' after the Reformation.
Synthesis: Today, following individualism, many think that people make the church. This is positive for the laity and marginalised groups but makes the church optional and dispensable.