21. It happens far otherwise with Christians; they receive their rule of faith from the Church, by whose authority and under whose guidance they are conscious that they have beyond question attained to truth. Consequently, as the Church is one, because Jesus Christ is one, so throughout the whole Christian world there is, and ought to be, but one doctrine: "One Lord, one faith;"(²²) "but having the same spirit of faith,"(²³) they possess the saving principle whence proceed spontaneously one and the same will in all, and one and the same tenor of action.