For a man’s complete sanctification, the body of the servant of the Lord must be united with the Body of Christ, and this is accomplished in the Mystery of Holy Communion. The true Body and the true Blood of Christ which we receive become part of the great Body of Christ.
Of course, for union with Christ, the mere conjoining of our body with the Body of Christ does not suffice. The consumption of the Body of Christ becomes beneficial when in spirit we strive towards Him and unite ourselves with Him. Receiving the Body of Christ, while turning away from Him in spirit, is like the contact with Christ which they had who struck Him and mocked and crucified Him. Their contact with Him served not for their salvation and healing, but for their condemnation.
But those who partake with piety, love and readiness to serve Him, closely unite themselves with Him and become instruments of His Divine will.
+ St. John the Wonderworker of Shanghai and San Francisco, “The Church as the Body of Christ,” Man of God: Saint John of Shanghai & San Francisco