According to the Reformation understanding, the church is everywhere where the Gospel is proclaimed, witnessed to together and lived. The Geneva reformer John Calvin wrote of the church: ‘For wherever we see the word of God preached and listened to sincerely, and the sacraments administered according to their institution by Christ, we cannot have any doubt that we have a church of God before us’ (Institutes of the Christian Religion IV,1,9).
The church exists independently of its institutional form. The number of church members is irrelevant, ‘[f]or where two or three are gathered in my name, I am there among them’ (Matthew 18:20).
Ecclesiology is the theological teaching on the church, independent of confessions and denominations (Catholic, Orthodox, Lutheran, Reformed, Anglican, etc.). Nevertheless, the various families of churches have often developed their own doctrines on the church.