1. Our communion with Jesus has three inseparable but distinct aspects (19‑C). We share divine life with him by adoption and the Spirit’s gift; this sharing begins in baptism (30‑H). We are commissioned by anointing with the Spirit to live our own lives as a share in his revelatory, redeeming life; this communion in cooperative work is established by confirmation (31‑A). And we are united bodily with Jesus and enlivened by his resurrection life; this is effected by the Eucharist (see LG 26; S.t., 3, q. 73, a. 3, ad 2).
2. Ordinary bodily digestion involves ingesting food and transforming nonliving material into one’s own living flesh. The Eucharist follows this pattern up to a point, then diverges remarkably. We ingest Jesus’ living, bodily self, but then he makes our mortal flesh come alive with his glorious resurrection life. “For ‘the partaking of the Body and Blood of Christ does nothing other than transform us into that which we consume’ ” (LG 26).9
3. The situation is not unlike the communion of marital love, which, as we shall see in question H below, is a sacrament of the communion of Jesus and the Church. From the communion of two in one flesh proper to marriage comes the special modality of a married couple’s cooperative action and even of their sharing in divine life. Similarly, communion with the Lord, at once bodily and mysterious, is necessary and effective in maintaining and perfecting the sharing in divine life and cooperation in human action which also unite us with Jesus (see Jn 6.44–58).
4. Acts of marital intercourse engaged in worthily “signify and promote that mutual self-giving by which spouses enrich each other with a joyful and thankful will” (GS 49). Holy Communion works in a similar manner. Worthy reception of the sacrament signifies and promotes the mutual self-giving of our Lord in glory and of us, as well as the imperfect contribution which we make to his fullness (see Eph 4.15–16; S.t., 3, q. 65, a. 3; q. 73, a. 3. ad 3; sup., q. 42).
People have difficulty in grasping this truth partly because of a tendency to separate personal reality from bodiliness. Many theologians whose accounts of the sacraments are not unorthodox nevertheless presuppose a false metaphysics, according to which the body is an instrument through which personal contact occurs.10 They assume that the person is a spiritual subject, the thinking and choosing self, who uses a body, very much as one uses an automobile. This metaphysical assumption is called “body-self dualism.”
But dualism is altogether false. A human person is not a mental self concealed in a body-object but a living human body who, among other things, thinks and chooses (see S.t., 1, q. 75, a. 4; q. 76, a. 1). The theological proof of the falsity of body-self dualism is that the Word who was from the beginning and whom we proclaim is the very same reality as was seen and heard by the apostles (see 1 Jn 1.1–2). If body-self dualism were true, the apostles would never have seen the Word Incarnate, but only a bodily sacrament of him.11
9. The internal quotation is annotated by note 55; St. Leo the Great, Serm. 63, 7; P.L., 54:357 C.
10. An example: E. Schillebeeckx, O.P., Christ the Sacrament of the Encounter with God (Kansas City: Sheed, Andrews and McMeel, 1963), 15: “When a man exerts spiritual influences on another, encounters through the body are necessarily involved.” Statements of this sort signal the assumption that the person really is the “inward man” or “interiority” which uses the body as an expression and instrument by which to “manifest itself.” The assumption is bad metaphysics. See Germain Grisez, “Dualism and the New Morality,” Atti del Congresso Internazionale Tommaso d’Aquino nel Suo Settimo Centenario, vol. 5, L’Agire Morale (Naples: Edizioni Domenicane Italiane, 1977), 323–30. A refutation of dualism and additional references to the literature: Germain Grisez and Joseph M. Boyle, Jr., Life and Death with Liberty and Justice: A Contribution to the Euthanasia Debate (Notre Dame and London: University of Notre Dame Press, 1979), 377–80. Theologians influenced by dualism will deny that they are dualists; they will insist upon the very close relationship of body and subject. This insistence would be unnecessary except for the dualistic assumption which they are rightly trying to overcome but wrongly cling to.
11. Hence the title of Schillebeeckx’s work on the sacraments, which stops short of saying simply that Jesus is God and reduces him to a sacrament of encounter with God; this is hardly: “The Word became flesh” (Jn 1.14).