The Real Presence of Jesus Christ in the Sacrament of the Eucharist: Basic Questions and Answers:
What are appropriate signs of reverence with respect to the Body and Blood of Christ?
The Body and Blood of Christ present under the appearances of bread and wine are treated with the greatest reverence both during and after the celebration of the Eucharist (cf. Mysterium Fidei, nos. 56-61). For example, the tabernacle in which the consecrated bread is reserved is placed "in some part of the church or oratory which is distinguished, conspicuous, beautifully decorated, and suitable for prayer" ( Code of Canon Law, Can. 938, §2).
According to the tradition of the Latin Church, one should genuflect in the presence of the tabernacle containing the reserved sacrament. In the Eastern Catholic Churches, the traditional practice is to make the sign of the cross and to bow profoundly. The liturgical gestures from both traditions reflect reverence, respect, and adoration. It is appropriate for the members of the assembly to greet each other in the gathering space of the church (that is, the vestibule or narthex), but it is not appropriate to speak in loud or boisterous tones in the body of the church (that is, the nave) because of the presence of Christ in the tabernacle.
Also, the Church requires everyone to fast before receiving the Body and Blood of Christ as a sign of reverence and recollection (unless illness prevents one from doing so). In the Latin Church, one must generally fast for at least one hour; members of Eastern Catholic Churches must follow the practice established by their own Church.
If someone without faith eats and drinks the consecrated bread and wine, does he or she still receive the Body and Blood of Christ?
If "to receive" means "to consume," the answer is yes, for what the person consumes is the Body and Blood of Christ. If "to receive" means "to accept the Body and Blood of Christ knowingly and willingly as what they are, so as to obtain the spiritual benefit," then the answer is no. A lack of faith on the part of the person eating and drinking the Body and Blood of Christ cannot change what these are, but it does prevent the person from obtaining the spiritual benefit, which is communion with Christ. Such reception of Christ's Body and Blood would be in vain and, if done knowingly, would be sacrilegious (1 Cor 11:29). Reception of the Blessed Sacrament is not an automatic remedy. If we do not desire communion with Christ, God does not force this upon us. Rather, we must by faith accept God's offer of communion in Christ and in the Holy Spirit, and cooperate with God's grace in order to have our hearts and minds transformed and our faith and love of God increased.