What is Holy Communion?
It is the true body and blood of our Lord Jesus Christ under the bread and wine, given to us Christians to eat and drink, as it was instituted by Christ himself.
Where is this written?
Matthew, Mark, Luke and Paul say:
Our Lord Jesus Christ, on the night in which he was betrayed, took bread, and when he had given thanks, he broke it and gave it to his disciples saying:
Take and eat, this is my body, which is given for you.
Do this in remembrance of me.
Again, after supper he took the cup, gave thanks, and gave it to them, saying:
Take and drink of it, all of you.
This cup is the new testament in my blood,
which is shed for you and for many for the forgiveness of sins.
Do this, as often as you drink it, in remembrance of me.
What is the benefit of such eating and drinking?
It is pointed out in these words: “Given and shed for you for the forgiveness of sins.” Through these words the forgiveness of sin, life, and salvation are given to us in the Sacrament, for where there is forgiveness of sin, there is also life and salvation.
How can the bodily eating and drinking produce such great benefits?
It is not the eating and drinking alone, but also the words that accompany it, “Given and shed for you for the forgiveness of sins.” These words, together with the eating and drinking, are the chief thing in the Sacrament, and those who believe them have what they say and declare, namely, the forgiveness of sins.
When is a person worthy to receive the Sacrament?
Fasting and other outward disciplines are indeed good preparation, but people are truly worthy and well prepared who believe these words, "Given and shed for you for the forgiveness of sins." But those who do not believe these words or who doubt them are unworthy and unprepared, for the words "for you" require truly believing hearts.
(from: The Small Catechism, by Martin Luther ©Reclaim Resources, Sola Publishing, 2011)