This is what Dr. Martin Luther wrote about Holy Communion, which he called the “Sacrament of the Alter” in his Small Catechism:
The Sacrament of the Altar (Holy Communion)
What is the Sacrament of the Altar (Holy Communion)?
It is the true body and blood of our Lord Jesus Christ under the bread and wine, instituted by Christ Himself for us Christians to eat and to drink.
Where is this written?
The holy Evangelists Matthew, Mark, Luke, and St. Paul write:
Our Lord Jesus Christ, on the night when He was betrayed, took bread, and when He had given thanks, He broke it and gave it to the disciples and said: “Take, eat; this is My body, which is given for you. This do in remembrance of Me.”
In the same way also He took the cup after supper, and when He had given thanks, He gave it to them, saying, “Drink of it, all of you; this cup is the new testament in My blood, which is shed for you for the forgiveness of sins. This do, as often as you drink it, in remembrance of Me.”
What is the benefit of this eating and drinking?
These words, “Given and shed for you for the forgiveness of sins,” show us that in the Sacrament forgiveness of sins, life, and salvation are given us through these words. For where there is forgiveness of sins, there is also life and salvation.
How can bodily eating and drinking do such great things?
Certainly not just eating and drinking do these things, but the words written here: “Given and shed for you for the forgiveness of sins.” These words, along with the bodily eating and drinking, are the main thing in the Sacrament. Whoever believes these words has exactly what they say: “forgiveness of sins.”
Who receives this sacrament worthily?
Fasting and bodily preparation are certainly fine outward training. But that person is truly worthy and well prepared who has faith in these words: “Given and shed for you for the forgiveness of sins.” But anyone who does not believe these words or doubts them is unworthy and unprepared, for the words “for you” require all hearts to believe.