communion n. [From Old French comunion, from Latin commūniō (“communion”), from cum (“with”) + mūnus (“gift”)] A joining together of minds or spirits.
San Francisco Archbishop Salvatore Cordileone explains why Catholics who dissent from Church teaching shouldn't present themselves for Communion. Note that Abp. Cordileone cites both Scripture and Tradition to back his points up [emphasis mine]:
Whoever ... 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. (1 Corinthians 11:27-29 RSVCE)
And this food is called among us Εὐχαριστία [the Eucharist], of which no one is allowed to partake but the man who believes that the things which we teach are true, and who has been washed with the washing that is for the remission of sins, and unto regeneration, and who is so living as Christ has enjoined. For not as common bread and common drink do we receive these; but in like manner as Jesus Christ our Saviour, having been made flesh by the Word of God, had both flesh and blood for our salvation, so likewise have we been taught that the food which is blessed by the prayer of His word, and from which our blood and flesh by transmutation are nourished, is the flesh and blood of that Jesus who was made flesh. (St. Justin Martyr, First Apology 66)
[H/T to LifeSite News!]