Calvin writes, “The pure ministry of the word and pure mode of celebrating the sacraments are, as we say, sufficient pledge and guarantee that we may safely embrace as church any society in which both these marks exist. The principle extends to the point that we must not reject it so long as it retains them, even if it otherwise swarms with many faults. What is more, some fault may creep into the administration of either doctrine or sacraments, but this ought not to estrange us from communion with the church. For not all articles of true doctrine are of the same sort (emphasis mine). Some are so necessary to know that they should be certain and unquestioned by all men as the principles of religion. Such are: God is one; Christ is God and the Son of God; our salvation rests in God’s mercy; and the like. Among the churches there are other articles of doctrine disputed which still do not break the unity of faith” (Institutes, 4:1:12; 2:1025).