The Church is incapable of forgiving any sin without Christ, and Christ is unwilling to forgive any sin without the Church. The Church cannot forgive the sin of one who has not repented, who has not been touched by Christ; Christ will not forgive the sin of one who despises the Church. What God has joined together, man must not separate. This is a great mystery, but I understand it as referring to Christ and the Church.
–Blessed Isaac of Stella (Twelfth Century)