The Sacrament of Holy Eucharist
Holy Eucharist is the name given to the Blessed Sacrament of the Altar in its twofold aspect of sacrament and Sacrifice of Mass, and in which Jesus Christ is truly present under the appearances of bread and wine.
In the Blessed Trinity, God the Father communicates His Divine Nature to God the Son, “the only begotten Son who is in the bosom of the Father” (John 1:18), while the Son of God, by virtue of the hypostatic union, communicates in turn the Divine Nature received from His Father to His human nature formed in the womb of the Virgin Mary (John 1:14), in order that thus as God-man, hidden under the Eucharistic Species, He might deliver Himself to His Church, who, as a tender mother, mystically cares for and nurtures in her own bosom this, her greatest treasure, and daily places it before her children as the spiritual food of their souls. Thus the Trinity, Incarnation, and Eucharist are really welded together like a precious chain, which in a wonderful manner links heaven with earth, God with man, uniting them most intimately and keeping them thus united. By the very fact that the Eucharistic mystery does transcend reason, no scientific explanation of it can come from us feeble humans.
Catholic doctrine consists in this, that in the Eucharist the Body and Blood of Jesus Christ, the God-man, are truly, really, and substantially present for the nourishment of our souls, by reason of the transubstantiation of the bread and wine into the Body and Blood of Christ, and that in this change of substances the unbloody Sacrifice of the New Testament is also contained.
On Holy Thursday, Our Lord ate the Paschal meal with His apostles. After having eaten, Our Lord with profound humility washed the feet of His apostles, exhorting them to practise the same humility and charity; afterwards, He gave them His Flesh and Blood under the appearance of bread and wine, for spiritual food and drink, thus instituting the Must Holy Sacrament of the Altar, the Sacrifice of the Mass, and the priesthood; for when He said to the apostles: Do this in commemoration of me, he ordained them priests.