Taken from holyspiritinteractive.comCatholics who have received their First Sacraments, who are not conscious of grave sin, and who have fasted for at least one hour are encouraged to devoutly and frequently receive Holy Communion.
This is very important:
To respond to this invitation we must prepare ourselves for so great and so holy a moment. St. Paul urges us to examine our conscience: "Whoever, therefore, eats the bread or drinks the cup of the Lord in an unworthy manner will be guilty of profaning the body and blood of the Lord. Let a man examine himself, and so eat of the bread and drink of the cup. For any one who eats and drinks without discerning the body eats and drinks judgment upon himself." Anyone conscious of a grave sin must receive the sacrament of Reconciliation before coming to communion. (CCC 1385)
Translation: taking this Sacrament with serious, unconfessed sin on the soul brings condemnation rather than salvation!
We are also required to fast for just one hour before receiving. Water and medicine do not break a fast. Catholics are obliged to receive this sacrament at least once per year, if possible during Easter (CCC 1388).
Non-Catholics are not ordinarily admitted to Holy Communion and are asked to pray that the action of the Holy Spirit will draw us closer together and begin to dispel the sad divisions which separate us (see CCC 1398-1401).
Why Can't Non-Catholics Receive Holy Communion?
Contrary to popular belief, the reason non-Catholics are asked to refrain from receiving Holy Communion is not because the Church wants anyone to feel excluded. The Church, in fact, has a certain responsibility to non-Catholics.
Because what makes us Catholic is our belief of Jesus’ True Presence in the Eucharist, it would be a disservice to allow non-Catholics to partake in this extraordinary union when they do not know or understand that which they are joining in. Why? Because they would not have been able to properly prepare themselves.
St. Justin Martyr wrote this in his apology to the emperor at Rome circa 150 AD:
We call this food Eucharist; and no one else is permitted to partake of it, except one who believes our teaching to be true….For not as common bread nor common drink do we receive these; but since Jesus Christ our Savior was made incarnate by the word of God and has both flesh and blood for our salvation, so too, as we have been taught, the food which has been made into the Eucharist by the Eucharistic prayer set down by Him, and by the change of which our blood and flesh is nourished, is both the Flesh and the Blood of that incarnated Jesus.
Circa 110, St. Ignatius of Antioch, who was a disciple of the Apostle John, wrote this concerning heretics:
They abstain from the Eucharist and from prayer, because they do not confess that the Eucharist is the Flesh of our Savior Jesus Christ, Flesh which suffered for our sins and which the Father, in His goodness, raised up again.
And from St. Cyril of Jerusalem, in a catechetical lecture he gave in the middle of the fourth century, we get this:
Do not, therefore, regard the bread and wine as simply that; for they are, according to the Master’s declaration, the Body and Blood of Christ. Even though the sense suggest to you the other, let faith make you firm. Do not judge in this matter by taste, but be fully assured by the faith, not doubting that you have been deemed worthy of the Body and Blood of Christ.
