The Eucharist thus appears as the culmination of all the sacraments in perfecting our communion with God the Father by identification with His only-begotten Son through the working of the Holy Spirit. With discerning faith a distinguished writer of the Byzantine tradition voiced this truth: in the Eucharist “unlike any other sacrament, the mystery [of communion] is so perfect that it brings us to the heights of every good thing: here is the ultimate goal of every human desire, because here we attain God and God joins Himself to us in the most perfect union.”
Precisely for this reason it is good to cultivate in our hearts a constant desire for the sacrament of the Eucharist. This was the origin of the practice of “spiritual Communion”, which has happily been established in the Church for centuries and recommended by saints who were masters of the spiritual life. Saint Teresa of Jesus wrote: “When you do not receive Communion and you do not attend Mass, you can make a spiritual Communion, which is a most beneficial practice; by it the love of God will be greatly impressed on you.”
Invisible Communion, though by its nature always growing, presupposes the life of grace, by which we become “partakers of the divine nature” (2 Pet 1:4), and the practice of the virtues of faith, hope and love. Only in this way do we have true communion with the Father, the Son, and the Holy Spirit. Nor is faith sufficient; we must persevere in sanctifying grace and love, remaining within the Church “bodily” as well as “in our heart”; what is required, in the words of Saint Paul, is “faith working through love” (Gal 5:6).
Keeping these invisible bonds intact is a specific moral duty incumbent upon Christians who wish to participate fully in the Eucharist by receiving the body and blood of Christ. The Apostle Paul appeals to this duty when he warns: “Let a man examine himself, and so eat of the bread and drink of the cup” (1 Cor 11:28). Saint John Chrysostom, with his stirring eloquence, exhorted the faithful: “I too raise my voice, I beseech, beg and implore that no one draw near to this sacred table with a sullied and corrupt conscience. Such an act, in fact, can never be called 'Communion', not even were we to touch the Lord's body a thousand times over, but 'condemnation', 'torment' and 'increase of punishment'.”
Along these same lines, the Catechism of the Catholic Church rightly stipulates that “anyone conscious of a grave sin must receive the sacrament of Reconciliation before coming to Communion.” I therefore desire to reaffirm that in the Church there remains in force, now and in the future, the rule by which the Council of Trent gave concrete expression to the Apostle Paul's stern warning when it affirmed that, in order to receive the Eucharist in a worthy manner, “one must first confess one's sins, when one is aware of mortal sin.”
The two sacraments of the Eucharist and Penance are very closely connected. Because the Eucharist makes present the redeeming sacrifice of the Cross, perpetuating it sacramentally, it naturally gives rise to a continuous need for conversion, for a personal response to the appeal made by Saint Paul to the Christians of Corinth: “We beseech you on behalf of Christ, be reconciled to God” (2 Cor 5:20). If a Christian's conscience is burdened by serious sin, then the path of penance through the sacrament of Reconciliation becomes necessary for full participation in the Eucharistic Sacrifice.
The judgment of one's state of grace obviously belongs only to the person involved, since it is a question of examining one's conscience. However, in cases of outward conduct which is seriously, clearly and steadfastly contrary to the moral norm, the Church, in her pastoral concern for the good order of the community and out of respect for the sacrament, cannot fail to feel directly involved. The Code of Canon Law refers to this situation of a manifest lack of proper moral disposition when it states that those who “obstinately persist in manifest grave sin” are not to be admitted to Eucharistic Communion.
(...) It is not possible to give Communion to a person who is not baptized nor to one who rejects the full truth of the faith regarding the Eucharistic mystery. Christ is the truth and He bears witness to the truth (cf. Jn 14:6; 18:37); the sacrament of His body and blood does not permit duplicity.
The Eucharist's particular effectiveness in promoting communion is one of the reasons for the importance of Sunday Mass. I have already dwelt on this and on the other reasons which make Sunday Mass fundamental for the life of the Church and of individual believers in my Apostolic Letter on the sanctification of Sunday Dies Domini. There I recalled that the faithful have the obligation to attend Mass, unless they are seriously impeded, and that Pastors have the corresponding duty to see that it is practical and possible for all to fulfil this precept. (...)