The sacraments are outward and visible signs of inward and spiritual grace, ordained by Christ Himself, as means whereby we receive the same, and pledges to assure us thereof. The principle of the sacraments is found in the whole Bible, and in its fulness in the New Testament, that is, in the Incarnation of the Word of God, Jesus Christ. God becomes Man so that man may become one with God. God assumes human nature in the Incarnation, all that pertains to man, human body, mind, soul, and spirit, so that human nature may be redeemed, sanctified, and glorified by God to share in the divine life.
God takes our human nature, divinises it, and gives it back to us in the sacraments, so that we may, in our own human nature, partake of God Himself. As the Fathers love to say: 'we become by grace what God is by nature.'
The Incarnation and the Sacraments are two expressions of one reality: God the Son becomes Man, and then takes that Hypostatic Union, human flesh united to the Divine Word, and conveys it to the members of His own Mystical Body, the Church, in and through the Sacraments.
This is why the Great Tradition teaches that the pre-eminent Sacraments of Holy Baptism and the Holy Eucharist are generally necessary to salvation: Baptism, as the Sacrament of New Birth, mystically unites us to the crucified and risen Christ and regenerates our human nature into the nature of the Son of God (St John 3.3-7, Romans 6.1-11, Galatians 3.22-29). We become children of God and members of Christ's Body in Baptism.
The Holy Eucharist, the Sacrament of the Lord's Body and Blood, nourishes us with the human nature and divinity of Christ unto everlasting life (St John 6.53-59, 1 Corinthians 10.14-22, 11.23-34). Our Lord's True Body and True Blood are really contained, really given, and really eaten, objectively, under the forms of bread and wine in the Eucharist, after an heavenly and supernatural manner, so that we may partake of Christ's human nature and be recreated by it.
Ours is a 'body religion,' the Church as the Body of Christ, the Religion of the Incarnation, which is made a reality in us sacramentally. There is only One Body of Christ, in the Incarnation, in the Eucharist, and in the Church, us.
Thus, man is a sacrament. Man is a composite being of body and soul, an outward and visible sign of an inward and spiritual reality. Man's outward sign is his body; man's inward and spiritual reality is his soul and spirit. Mankind is a living sacrament: he simultaneously exists as material and spiritual, physical and supernatural, united together in one cohesive entity. When the soul leaves the body, death occurs, which is for man an unnatural state not intended by God in His first creation of us. Man was created to be forever alive, forever immortal in a sacramental state.