To speak of the Eucharist and the Trinity is to delve into the very depths of the mystery of God. On the one hand, the Eucharist is holy not because it is ordered to holiness, but because the Eucharist is holiness itself: it is the real, substantial presence of Christ. Participation in the Eucharist is participation in the divine life itself. On the other hand, the Trinity is the divine life itself. It is the relationship of the three Persons of God: Father, Son, and Holy Spirit. Participation in the Trinity is the divine life itself. Neither the Eucharist nor the Trinity is known to us by natural human reason. Both of these mysteries are revealed to us in Jesus Christ, God and man, the Incarnation, whose presence in the Eucharist—body, blood, soul, and divinity—does not alter His relationship to the Father and Spirit in the Trinity and whose kenosis does not in any way diminish His Trinitarian existence.

The Eucharist allows for an overpowering intimacy with Christ, an intimacy in this life and in the life hereafter. Jesus said: "He who eats my flesh and drinks my blood abides in me and I in him. As the living Father sent me, and I live because of the Father, so he who eats me will live because of me" (John 6:56-57). Life in Christ is the foundation of the sacraments. It is to the Eucharist that the other six sacraments are directed and fulfilled (Presbyterorum Ordinis, n. 5, and St. Thomas Aquinas, Summa Theologiae, III, q. 73, art. 3). In the Incarnation, mankind has been lifted up by Christ’s obedient sacrifice to share in His divine life, to be one with the second Person of the Trinity, and therefore to enter mysteriously the inner life of God. In the sharing of holy communion, men share in the life of the Trinity.

The Trinity is the Author of the divine economy, and the ultimate end of that economy is union with the same Trinity. This is expressed by the Son as He prays to the Father "that they may be perfectly one" (John 17:21-23), and it is the fruit of the parousia that "God may be all in all" (1 Cor 15:28). The Christian life, then, is both a communal and individual endeavor to forge communion with one another and with the divine Persons, whose relationship is the paradigm for all relationship in the cosmos. Thus, Holy Communion not only effects what it signifies, but is in fact what it signifies: Holy Communion between God and man. In the Eucharist, men eat the flesh and blood of Jesus Christ, whose very Self and whose very self-sacrifice, bear up men into communion with the Trinity.

The Eucharist and the Trinity are thoroughly united in the divine economy. It is an economy in which men actually share, albeit mysteriously. To say that we share mysteriously is not to say that we share obliquely, immaterially, or trivially—just the opposite is true—but it is to say that our human expression cannot contain the divine reality wherein we find ourselves in communion with God: Creator, Redeemer, and Sanctifier. It is the second Person of the Trinity who is incarnated among men in order that He might return mankind to communion with the Trinity. That communion is established in the Sacrifice of the Mass, wherein we represent Calvary and share in His body and blood, so that He might reconcile all things to Himself and present us blameless and irreproachable before the Triune God (Col 1:20-22).