Catholics attend Mass (at least) weekly. A central part of Mass is the Liturgy of the Eucharist during which we receive Communion. Of the seven sacraments (see The Sacraments), the Sacrament of Holy Communion is received most often.
Jesus was very clear and not ambiguous when he gave the first Catholic bishops (the Apostles) this sacrament:
Then he took the bread, said the blessing, broke it, and gave it to them, saying, “This is my body, which will be given for you; do this in memory of me.” And likewise the cup after they had eaten, saying, “This cup is the new covenant in my blood, which will be shed for you.”
Jesus was not speaking figuratively. He meant what he said – “this is my body.” Jesus also said “do this in memory of me,” commanding the Apostles and their successors to repeat this act of consecration and giving them the authority to do so. Catholic bishops and priests maintain that authority through an unbroken line of succession.
When a Catholic bishop or priest at any Mass worldwide consecrates bread and wine, those elements are literally transformed into the body and blood of Christ. This moment is often observed by the ringing of sanctus bells in many Catholic churches. The Holy Body and Precious Blood maintain only the appearance of bread and wine, just as they did at the last supper. To claim anything else is to dispute what Jesus said!
By consuming His Holy Body and Precious Blood we unite ourselves with Christ, grow in likeness to Him, sanctify our own body, remove the personal guilt of venial sins and receive other graces. Jesus also made the importance of this clear:
Jesus said to them, “Amen, amen, I say to you, unless you eat the flesh of the Son of Man and drink his blood, you do not have life within you. Whoever eats my flesh and drinks my blood has eternal life, and I will raise him on the last day. For my flesh is true food, and my blood is true drink. Whoever eats my flesh and drinks my blood remains in me and I in him.”
How wonderful this gift is! This is the Lamb of God who takes away the sins of the world. Happy are those who are called to his supper.
His Body and Blood may be consumed only by those of the proper disposition. The recipient must fully understand and accept the sacrament without qualification (i.e. be Catholic), may not have separated themselves from God (i.e. committed any non-absolved mortal sin), must have fasted and be eligible (i.e. not received Communion earlier that day – in most circumstances). Again, scripture is clear:
Therefore whoever eats the bread or drinks the cup of the Lord unworthily will have to answer for the body and blood of the Lord. A person should examine himself, and so eat the bread and drink the cup. For anyone who eats and drinks without discerning the body, eats and drinks judgment on himself.
His Body and Blood must be, and are, respected with the greatest possible reverence. There are protocols as to how the Host is distributed. Procedures have been established for unfortunate accidental situations. This IS the Body and Blood of our Lord and we act at all times in accordance of that fact and nothing less.
Finally, every Catholic church has a tabernacle in which undistributed Eucharist is reserved (stored). This is often near the altar with a red lamp nearby. This tabernacle lamp is lit to indicate and honor the presence of our Lord. When the lamp is lit, we kneel briefly on our right knee (genuflect) out of respect before entering a pew for worship.
When you have received Him, stir up your heart to do Him homage; speak to Him about your spiritual life, gazing upon Him in your soul where He is present for your happiness; welcome Him as warmly as possible, and behave outwardly in such a way that your actions may give proof to all of His Presence.
St. Francis de Sales