Conduct in Public Worship. 1 Cor. 11, 1–34
Worthy and unworthy communicants: V. 28. But let a man examine himself, and so let him eat of that bread and drink of that cup. V. 29. For he that eateth and drinketh unworthily eateth and drinketh damnation to himself, not discerning" the Lord's body.
It follows, then, for every earnest Christian: But let a man examine himself, make a careful test of his own mind and attitude, explore all the secret recesses of his heart, not, as some commentaries say, to see whether he is religiously and morally qualified, personally worthy of being a guest of the Lord's, but, as our liturgical formula very properly says, to see whether he heartily repents of his sins, believes in Jesus Christ, and sincerely and earnestly purposes to amend his sinful life.
Having made this examination, preferably with the aid of the questions in the Fifth Chief Part, in the Table of Duties, and in the Christian Questions offered in our Small Catechism, a Christian may come and partake of God's meal of grace. The purpose of the admonition, therefore, is not to deter and scare away such Christians in whom self-examination reveals many sins in thoughts, words, and deeds, but to stimulate the right desire for the grace of God, the need, of which this self-exploration has shown to exist. (Compare Luther, 12, 1342-1351).
"Therefore we should here learn diligently and mark that such persons do not receive the Sacrament unworthily as say and confess they are poor sinners, feel various temptations.… If you did not want to receive the Sacrament unless you were free from all sins, it would follow that you would never go to the Sacrament. But they that knowingly continue in sins receive the venerable Sacrament unworthily; as, murderous hatred of their neighbor, murder, fornication, adultery, and other, similar public transgressions, and do not purpose to discontinue them. For the Sacrament has been instituted by Christ the Lord, not that people should remain in sins, but that they should obtain forgiveness and grow in sanctity. ...
"I can speak with authority of what results follow if a person abstains from the Sacrament for a time; I have also been in such fire of the devil that I became estranged from the venerable Sacrament, and that I attended with the greater unwillingness, the longer this lasted. Be sure to beware of this and get into the habit of going often, especially if you are fit to go, that is, if you find that your heart, on account of your sins, is heavy and shy, in order that you may not forget our Lord and Savior Jesus Christ, but remember His sacrifice and death; for otherwise He asks nothing of us" (Luther, 13a, 311. 315).
But of the unworthy the apostle says: For he that eats and drinks unworthily, judgment, condemnation, he eats and drinks to himself, because he does not discern, discriminate, the body of Christ. He makes no distinction between an ordinary meal and this heavenly meal; he does not realize that the true body and blood of his Savior are here present, and that for this reason a thoughtless use of the Sacrament is blasphemy and results in the final righteous punishment of God. For he that approaches the table of the Lord in such a spirit of frivolousness will indeed also receive the body and blood of Christ in, with, and under the bread and wine, but not as that of his Redeemer, rather as that of his Judge, who will, on the last day, demand an account of him with sharp reckoning, since the outward behavior is only an indication and demonstration of the unbelief of the heart.
"We teach, believe, and confess also that there is only one kind of unworthy guests, those namely who do not believe, concerning whom it is written, John 3, 18: 'He that believeth not is condemned already,' And this judgment becomes greater and more grievous, being aggravated by the unworthy use of the Holy Supper, 1 Cor. 11, 29" (Concordia Triglotta, 813; compare Wittenberg Concordia, 977; Solid Declaration, 993).