11 After pondering all this long and seriously before God We consider it part of Our pastoral duty to explain to the entire flock of Christ through this Encyclical Letter the doctrine of the Mystical Body of Christ and of the union in this Body of the faithful with the divine Redeemer; and then, from this consoling doctrine, to draw certain lessons that will make a deeper study of this mystery bear yet richer fruits of perfection and holiness. Our purpose is to throw an added ray of glory on the supreme beauty of the Church; to bring out into fuller light the exalted supernatural nobility of the faithful who in the Body of Christ are united with their Head; and finally, to exclude definitely the many current errors with regard to this matter.
Source: Mystici Corporis Christi (Vatican.va)