The Sacrament of the Altar is a mark of the Church. Luther expounds upon this fact in his “Sermon on Confession and the Sacrament” from 1524. You’ll also note that Luther states that those who receive the Sacrament can be seen as those who confess God’s name, are unashamed of His Word and are willing to suffer for the right practice of it. Therefore we can rightly confess that the reception of the Sacrament is a sign of common faith and life in Christ.

It is also beautiful that God so rules and orders things in such a way that this Sacrament is not without persecution, for He has instituted it to be a sign and mark of Christendom, so that people can know who we are. If we did not have [this Sacrament], people would not know where to find Christians, who the Christians are, and where the Gospel has produced fruit. But when we go to the Sacrament, people can see who the people are who have heard the Gospel. Then they can pay attention to whether we live as Christians. So this is a mark by which we are recognized as those who confess God’s name and are unashamed of His Word.

Now when the pope sees that I go to the Sacrament and receive both kinds according to the Gospel, it is a testimony that I cling to the Gospel. Then if he becomes angry and wants to slay me, that is just the way it happened at first in Christendom, when Christians confessed God with this same mark. Our bishops have forbidden both kinds [in the Sacrament] contrary to Christ’s ordinance and command. If we want to confess Christ now, then we much receive nothing else than both kinds, so that people will know that we are Christians and value the Word of God highly. If they slay us for this, then we should endure it; God will give us our lives back in abundance. Therefore, it is right that we are persecuted for this, otherwise, if we were honored for it, it would not be a true confession. So we remain in the correct situation, that we must expect shame and disgrace and even death for the Lord’s sake, just as it happened in the early church.

Luther’s Works, Vol. 76 Church Postil II. Concordia Publishing House, 2013, pp. 440-441.