From A Layman’s Guide to the Liturgy by Burnell F. Eckardt, Jr.

Why do we Worship on Sunday?
Actually, in apostolic times, the Church was at prayer together daily. According to Acts 2: "They continued steadfastly in the
apostles’ doctrine and fellowship: the breaking of the bread and the prayers." Even so, they reserved Sunday for the high feast,
inasmuch as they recognized Sunday, the first day of the week, as the day when Christ arose from the dead. The Sabbath had
been Saturday previously, of course, but this was fulfilled when Christ rested in the tomb on Holy Saturday. This is why the Apostle declares that Sabbaths are a shadow of things to come, but the substance is of Christ. So, therefore, Sunday became the Church’s “high” day of worship, since Christ Himself not only arose on Sunday, but made His subsequent resurrected appearances also on Sundays
throughout the forty days leading to His ascension.
Then came Pentecost, the fiftieth day from Easter, also a Sunday. So it was Christ Himself who shifted the thinking of His people toward Sunday as the chief of days. Moreover, since, according to St. Luke’s Gospel, He was recognized by the Emmaus disciples (on Sunday) in the breaking of the bread, and that phrase is repeated in Acts (see above), so it was fitting that Sunday be also the chief day on which the Holy Sacrament was offered to the people.
So it was, throughout the ages, that Holy Christendom, whether or not they assembled also on other days of the week, would always assemble every Sunday (which, biblically, begins on Saturday night), in order especially to receive the Holy Sacrament in the Mass.
Therefore, the orders of Matins and Vespers, as well as other non-Communion services, were really never intended as replacements for the Mass on Sunday morning. Rather, they were used either on weekdays or as pre-sacramental services. But Sunday was reserved especially for high worship, that is, for the reception of the Holy Supper.
Why is Holy Communion sometimes called Mass?
There are actually many different names for the service of the Holy Sacrament. It is called the Eucharist, the Holy Supper, the Holy Communion, the Lord’s Supper, the Sacrament of the Altar, and the Mass. In the New Testament and early church times it was called the Breaking of the Bread.
The term Mass (Latin, missa) is perhaps the term with most widespread use throughout Christendom. It is also a source of controversy among Protestants because of its regular association with Roman Catholicism. The Lutheran Reformation renounced the Roman Mass as “the greatest and most horrible abomination, as it directly and powerfully conflicts with this chief article (of justification by faith in Christ).”
Yet the context of this statement will determine what it is that is abominable about the Roman Mass, for Luther’s quote continues: “...it has been held that this sacrifice of work of the Mass, even though it be rendered by a wicked scoundrel, frees men from sins, both in this life and also in purgatory; while only the Lamb of God shall and must do this” (ibid). Thus it is clear that what Luther opposed was the Roman idea of Mass as an act or work of man, essentially of re-sacrificing the body of Christ for sins. For Rome, the benefits of the Mass were effected by the work that the priest performed. For Luther and the Lutherans, the benefit was seen in the words, “Given and shed for you, for the remission of sins.” Thus, in the Mass, the Sacrament was to be received orally by the communicants in order for them to benefit from it.
Yet the term Mass was never abandoned on the Lutheran side. Indeed the Lutheran Confessions declare, “We do not abolish the Mass but religiously keep and defend it. In our churches, Mass is celebrated every Sunday and on other festivals, when the sacrament is offered to those who wish for it after they have been examined and absolved. We keep traditional liturgical forms such as the order of the lessons, prayers, vestments, etc.
In America, the term has been looked on with suspicion among many Lutherans, which is likely due to a long-held bias against anything “Catholic.” This bias is unfortunate especially because it leads to the preference of tendencies and terms which are in much more abundant use among churches which deny altogether the real presence of Christ in the Sacrament. Dr. C. F. W. Walther, founding father of the Missouri Synod, had this to say about such a bias: “It is a pity and dreadful cowardice when a person sacrifices the good ancient church
customs to please the deluded American sects, lest they accuse one of being papistic!”
Since we agree that the Sacrament is truly the Body and Blood of Christ—a point of agreement with Rome, and of disagreement with
Methodists, Baptists, and others—and since historically, confessing Lutherans have not shunned the use of the term Mass, therefore we
ought not be ashamed to use it, if only to distinguish ourselves from anyone who would deny that the bread is truly Christ’s Body, and the
wine is truly His Blood.
Actually, in apostolic times, the Church was at prayer together daily. According to Acts 2: "They continued steadfastly in the
apostles’ doctrine and fellowship: the breaking of the bread and the prayers." Even so, they reserved Sunday for the high feast,
inasmuch as they recognized Sunday, the first day of the week, as the day when Christ arose from the dead. The Sabbath had
been Saturday previously, of course, but this was fulfilled when Christ rested in the tomb on Holy Saturday. This is why the Apostle declares that Sabbaths are a shadow of things to come, but the substance is of Christ. So, therefore, Sunday became the Church’s “high” day of worship, since Christ Himself not only arose on Sunday, but made His subsequent resurrected appearances also on Sundays
throughout the forty days leading to His ascension.
Then came Pentecost, the fiftieth day from Easter, also a Sunday. So it was Christ Himself who shifted the thinking of His people toward Sunday as the chief of days. Moreover, since, according to St. Luke’s Gospel, He was recognized by the Emmaus disciples (on Sunday) in the breaking of the bread, and that phrase is repeated in Acts (see above), so it was fitting that Sunday be also the chief day on which the Holy Sacrament was offered to the people.
So it was, throughout the ages, that Holy Christendom, whether or not they assembled also on other days of the week, would always assemble every Sunday (which, biblically, begins on Saturday night), in order especially to receive the Holy Sacrament in the Mass.
Therefore, the orders of Matins and Vespers, as well as other non-Communion services, were really never intended as replacements for the Mass on Sunday morning. Rather, they were used either on weekdays or as pre-sacramental services. But Sunday was reserved especially for high worship, that is, for the reception of the Holy Supper.
Why is Holy Communion sometimes called Mass?
There are actually many different names for the service of the Holy Sacrament. It is called the Eucharist, the Holy Supper, the Holy Communion, the Lord’s Supper, the Sacrament of the Altar, and the Mass. In the New Testament and early church times it was called the Breaking of the Bread.
The term Mass (Latin, missa) is perhaps the term with most widespread use throughout Christendom. It is also a source of controversy among Protestants because of its regular association with Roman Catholicism. The Lutheran Reformation renounced the Roman Mass as “the greatest and most horrible abomination, as it directly and powerfully conflicts with this chief article (of justification by faith in Christ).”
Yet the context of this statement will determine what it is that is abominable about the Roman Mass, for Luther’s quote continues: “...it has been held that this sacrifice of work of the Mass, even though it be rendered by a wicked scoundrel, frees men from sins, both in this life and also in purgatory; while only the Lamb of God shall and must do this” (ibid). Thus it is clear that what Luther opposed was the Roman idea of Mass as an act or work of man, essentially of re-sacrificing the body of Christ for sins. For Rome, the benefits of the Mass were effected by the work that the priest performed. For Luther and the Lutherans, the benefit was seen in the words, “Given and shed for you, for the remission of sins.” Thus, in the Mass, the Sacrament was to be received orally by the communicants in order for them to benefit from it.
Yet the term Mass was never abandoned on the Lutheran side. Indeed the Lutheran Confessions declare, “We do not abolish the Mass but religiously keep and defend it. In our churches, Mass is celebrated every Sunday and on other festivals, when the sacrament is offered to those who wish for it after they have been examined and absolved. We keep traditional liturgical forms such as the order of the lessons, prayers, vestments, etc.
In America, the term has been looked on with suspicion among many Lutherans, which is likely due to a long-held bias against anything “Catholic.” This bias is unfortunate especially because it leads to the preference of tendencies and terms which are in much more abundant use among churches which deny altogether the real presence of Christ in the Sacrament. Dr. C. F. W. Walther, founding father of the Missouri Synod, had this to say about such a bias: “It is a pity and dreadful cowardice when a person sacrifices the good ancient church
customs to please the deluded American sects, lest they accuse one of being papistic!”
Since we agree that the Sacrament is truly the Body and Blood of Christ—a point of agreement with Rome, and of disagreement with
Methodists, Baptists, and others—and since historically, confessing Lutherans have not shunned the use of the term Mass, therefore we
ought not be ashamed to use it, if only to distinguish ourselves from anyone who would deny that the bread is truly Christ’s Body, and the
wine is truly His Blood.