The often-groundless views of worship in America are contrasted here with
  the views of the founder of the Lutheran Reformation. Luther addresses the
  questions: Why is there worship? Did Adam worship? Did Adam have to go to
  church? Who was the preacher? In the context of life before the fall into sin
  what was worship like? It didn't last that long, yet, nevertheless there was
  true worship.
  More than the subject of "Church and Ministry," Luther wrote on
  the more practical subject of true worship. What could be truer about worship
  than worship before the fall into sin? In view of the corruption of worship by
  Pope, the "late" Luther (1535-1545) was engrossed in the subject of
  true worship.
  Luther may have been the first author to write so extensively on worship
  before the fall into sin. All that Luther has to say about worship, and there
  is a great deal, must be predicated on his understanding of worship before the
  fall into sin. Needless to say, after the fall, the character of worship
  changed.
  Luther's thoughts about worship are focused on Genesis 2:3 "And God
  blessed the seventh day and sanctified it, because on it He had rested from
  all His work, which God created, so that He made it."
  God made the Sabbath for man
  Luther quotes Matthew 12 and Mark 2 to support his interpretation of Gen.
  2:3 that God made the Sabbath for man before the fall into sin. "For the
  Son of man is Lord even of the Sabbath day." (Matthew 12:8) "And he
  said unto them, The Sabbath was made for man, and not man for the Sabbath: 28
  Therefore the Son of man is Lord also of the Sabbath." (Mark 2:27-28)
  Luther points out that Moses doesn't say anything about man in Gen. 2:3 but
  that God blessed the Sabbath and sanctified it for Himself. This means the
  Sabbath is set aside for divine worship.
  The seventh day was made holy by God till the end
  of time
  Luther makes no comment about the necessity of which day is chosen for
  worship as long as it is once every seven days.
  "This has the special purpose of making us understand that the seventh
  day in particular should be devoted to divine worship. For "holy" is
  that which has been set-aside for God and has been removed from all secular
  uses. Hence to sanctify means to set aside for sacred purposes, or for the
  worship of God. In this manner Moses rather frequently employs the expression,
  also of sacred vessels." (LW1:79)
  Adam would have always kept the seventh day holy
  "It follows, therefore, from this passage that if Adam had remained in
  the state of innocence, he nevertheless would have held the seventh day
  sacred. That is, on this day he would have given his descendants instructions
  about the will and worship of God; he would have praised God; he would have
  given thanks; he would have sacrificed, etc. . . Indeed, even after the Fall
  he kept this seventh day sacred; that is, on this day he instructed his
  family, of which the sacrifices of his sons Cain and Abel give the proof.
  Therefore from the beginning of the world the Sabbath was intended for the
  worship of God." (LW1:79)
  The human race was intended to be immortal as proven
  by the command to worship
  "Moreover, this also implies the immortality of the human race, as the
  Letter to the Hebrews (8:11) learnedly expounds concerning God's rest on the
  basis of Ps. 95:11: 'They shall not enter into My rest.' For God's rest is
  eternal. Adam would have lived for a definite time in Paradise, according to
  God's pleasure; then he would have been carried off to that rest of God, which
  God, through the sanctifying of the Sabbath, wished not only to symbolize for
  men but also to grant to them. Thus the physical life would have been blissful
  and holy, spiritual and eternal." (LW1:80)
  The Sabbath command remains for the church
  "Now we wretched men have lost that bliss of our physical life through
  sin, and while we live we are in the midst of death. And yet, because the
  Sabbath command remains for the church, it denotes that spiritual life is to
  be restored to us through Christ. And so the prophets have carefully searched
  those passages in which Moses intimates the resurrection of the flesh and life
  immortal." (LW1:80)
  Man is created for worship
  "Then it is also shown here that man was especially created for the
  knowledge and worship of God; for the Sabbath was not ordained for sheep and
  cows but for men, that in them the knowledge of God might be developed and
  might increase." (LW1:80)
  The Seventh day is set-aside for the Word of God
  "On the seventh day He wanted men to busy themselves both with His
  Word and with the other forms of worship established by Him, so that we might
  give first thought to the fact that this nature was created chiefly for
  acknowledging and glorifying God." (LW1:80)
  The Existence of God's Word proves eternal life
  "Moreover, this is also written that we might preserve in our minds a
  sure hope of the future and eternal life. All the things God wants done on the
  Sabbath are clear signs of another life after this life. Why is it necessary
  for God to speak with us through His Word if we are not to live in a future
  and eternal life? If we are not to hope for a future life, why do we not live
  like people with whom God does not speak and who do not know God? But because
  the Divine Majesty speaks to man alone and man alone knows and apprehends God,
  it necessarily follows that there is another life after this life; to attain
  it we need the Word and the knowledge of God. For this temporal and present
  life is a physical life, such as all the beasts live that do not know God and
  the Word." (LW1:80)
  "Therefore that God gives His Word, that He commands us to occupy
  ourselves with the Word, that He issues orders for sanctifying the Sabbath and
  for His worship-and this clearly proves that there remains a life after this
  life and that man was created not for this physical life only, like the other
  animals, but for eternal life, just as God, who has ordered and ordained these
  practices, is eternal." (LW1:81)
  The seventh day is for preaching
  "Early in the morning of the seventh day, which had been sanctified by
  the Lord, God speaks with Adam, gives him directions concerning His worship,
  and forbids him to eat the fruit of the tree of the knowledge of good and
  evil. This is the real purpose of the seventh day: that the Word of God be
  preached and heard. Henceforth both in the Scripture and in common usage the
  practice remained that the morning time was set aside for prayer and
  preaching, as Ps. 5:3 says: 'In the morning I shall stand before Thee, and I
  shall see.'" (LW1:81)
  The Tree of Knowledge was to be the center of Adam's
  Worship
  "Today in our churches we have an altar for the administration of the
  Eucharist, and we have platforms or pulpits for teaching the people. These
  objects were built not only to meet a need but also to create a solemn
  atmosphere. But this tree of the knowledge of good and evil was Adam's church,
  altar, and pulpit." (LW1:95)
  "So, then, this tree of the knowledge of good and evil, or the place
  where trees of this kind were planted in large number, would have been the
  church at which Adam, together with his descendants, would have gathered on
  the Sabbath day." (LW1:105)
  Adam worshiped God by obeying the command not
  to eat from the Tree
  "Therefore let us learn that some external form of worship and a
  definite work of obedience were necessary for man, who was created to have all
  the other living creatures under his control, to know his Creator, and to
  thank Him." (LW1:95)
  ". . . while the tree of the knowledge of good and evil is forbidden,
  the outward worship of the future church is established by divine
  authority-the worship in which they would have borne witness of their
  obedience to God if they had avoided the devil's snares." (LW1:140)
  "The tree was not poisonous; but, as we said above at great length, it
  was a tree of divine worship, for man to bear witness through his obedience
  that he knew, honored, and feared his God. For God saw that everything He had
  made was very good." (LW1:227)
  The Tree was Gospel and Law
  "'For the complete text reads (1 Tim. 1:9-10): "The Law has not
  been given for the just person, but for murderers, adulterers, etc.' From this
  there follows nothing else than that Paul is speaking about that Law which was
  given after sin, and not about this Law which the Lord gave when Adam was
  still guiltless and righteous. For the righteous, he says, no Law was given;
  therefore it follows undeniably that the Law was given to wicked and sinful
  nature." (LW1:108)
  "'The Word which the Lord had spoken to Adam was: "Do not eat
  from the tree of the knowledge of good and evil.' For Adam this Word was
  Gospel and Law; it was his worship; it was his service and the obedience he
  could offer God in this state of innocence." (LW1:146)
Note: The reference
"Luther's Works" and "LW" in all quotations and the body of
this article refer (via volume and page number(s)) to the American Edition of
Luther's Works, jointly published by Fortress Press and Concordia Publishing
House.