Pope Pius XII
Mystici Corporis Christi §83
Mystici Corporis Christi: On the Mystical Body of Christ
83 The Sacrament of the Eucharist is itself a striking and wonderful figure of the unity of the Church, if we consider how in the bread to be consecrated many grains go to form one whole, and that in it the very Author of supernatural grace is given to us, so that through Him we may receive the spirit of charity in which we are bidden to live now no longer our own life but the life of Christ, and to love the Redeemer Himself in all the members of His social Body.
Source: Mystici Corporis Christi (Vatican.va)