Non-Catholics should not be offended if they ever attend a Catholic Mass for a funeral or wedding of their friends and are not able to receive Holy Communion. For Catholics, the Eucharist is not a symbol like so many other Christians believe, but it is rather what Jesus says it is… truly His Body and Blood physically present under the appearance of bread and wine. Receiving Holy Communion means that we accept Christ completely… and are united to His Church, His Body, by means of this communion and believe everything that He has passed on to us through His Church. If it is just a symbol, that it really isn’t that important to receive anyway as we can just be united to Christ spiritually by an act of Faith. But if it is truly the Body and Blood of Christ and you authentically believe this, then shouldn’t you really consider becoming a Catholic so that you can receive Him physically?
In John’s gospel, Jesus summarized the reasons for receiving Communion when he said:
“Truly, truly, I say to you, unless you eat the flesh of the Son of man and drink his blood, you have no life in you; he who eats my flesh and drinks my blood has eternal life, and I will raise him up at the last day. For my flesh is real food, and my blood is real drink. He who eats my flesh and drinks my blood abides in me, and I in him. As the living Father sent me, and I live because of the Father, so he who eats me will live because of me. This is the bread which came down from heaven, not such as the fathers ate and died; he who eats this bread will live forever” (John 6:53–58).
“And when He had taken some bread and given thanks, He broke it and gave it to them, saying, “This is My body which is given for you; do this in remembrance of Me.” Lk 22:19
“He who eats My flesh and drinks My blood has eternal life, and I will raise him up on the last day.” Jn 6:54
“Therefore whoever eats the bread or drinks the cup of the Lord in an unworthy manner, shall be guilty of the body and the blood of the Lord. But a man must examine himself, and in so doing he is to eat of the bread and drink of the cup. For he who eats and drinks, eats and drinks judgment to himself if he does not judge the body rightly.” 1Cor11:27-29
Non-Catholics don't have confession. If the non-Catholic is living a life in mortal sin, and they take the Eucharist the non-Catholic is taking the body and blood of Christ unworthily and could bring condemnation upon themselves. If a Catholic is living in mortal sin they need to go to confession, and do what the church expects to be in full union with the church before they receive the Eucharist.
Catholic Answers Who Can Receive Communion?