A selection from Luther's Large Catechism, about the Third Commandment:
Remember the Sabbath day by keeping it holy.
79 The word holiday is used for the Hebrew word sabbath, which properly means “to rest,” that is, to cease from labor. Therefore, we usually say, “to stop working.” Or “Sanctify the Sabbath.” 80 Now, in the Old Testament, God set apart the seventh day and appointed it for rest [Genesis 2:3]. He commanded that it should be regarded as holy above all other days. This commandment was given only to the Jewish people for this outward obedience, that they should stop toilsome work and rest. In that way both man and beast might recover and not be weakened by endless labor [Exodus 20:8–11]. 81 Later, the Jewish people restricted the Sabbath too closely and greatly abused it. They defamed Christ and could not endure in Him the same works that they themselves would do on that day, as we read in the Gospel [Matthew 12:11]. They acted as though the commandment were fulfilled by doing no manual work whatsoever. This, however, was not the meaning. But, as we shall hear, they were supposed to sanctify the holy day or day of rest.
82 This commandment, therefore, in its literal sense, does not apply to us Christians. It is entirely an outward matter, like other ordinances of the Old Testament. The ordinances were attached to particular customs, persons, times, and places, but now they have been made matters of freedom through Christ [Colossians 2:16–17].
83 The simpleminded need to grasp a Christian meaning about what God requires in this commandment. Note that we don’t keep holy days for the sake of intelligent and learned Christians. (They have no need of holy days.) We keep them first of all for bodily causes and necessities, which nature teaches and requires. We keep them for the common people, manservants and maidservants, who have been attending to their work and trade the whole week. In this way they may withdraw in order to rest for a day and be refreshed.
84 Second, and most especially, on this day of rest (since we can get no other chance), we have the freedom and time to attend divine service. We come together to hear and use God’s Word, and then to praise God, to sing and to pray [Colossians 3:16].
85 However, this keeping of the Sabbath, I point out, is not restricted to a certain time, as with the Jewish people. It does not have to be just on this or that day. For in itself no one day is better than another [Romans 14:5–6]. Instead, this should be done daily. However, since the masses of people cannot attend every day, there must be at least one day in the week set apart. From ancient times Sunday ‹the Lord’s Day› has been appointed for this purpose. So we also should continue to do the same, in order that everything may be done in an orderly way [1 Corinthians 14:40] and no one may create disorder by starting unnecessary practices.
86 This is the simple meaning of the commandment: People must have holidays. Therefore, such observances should be devoted to hearing God’s Word so that the special function of this day of rest should be the ministry of the Word for the young and the mass of poor people [Nehemiah 8:2–3, 8]. Yet the resting should not be strictly understood to forbid any work that comes up, which cannot be avoided.
87 So when someone asks you, “What is meant by the commandment: You shall sanctify the holy day?” Answer like this, “To sanctify the holy day is the same as to keep it holy.” “But what is meant by keeping it holy?” “Nothing else than to be occupied with holy words, works, and life.” For the day needs no sanctification for itself. It has been created holy in itself. But God desires the day to be holy to you. Therefore, it becomes holy or unholy because of you, whether you are occupied on that day with things that are holy or unholy.
88 How, then, does such sanctification take place? Not like this: sitting behind the stove and doing no rough work, or adorning ourselves with a wreath and putting on our best clothes. But as said above, we occupy ourselves with God’s Word and exercise ourselves in the Word.
89 Indeed, we Christians ought always to keep such a holy day and be occupied with nothing but holy things. This means we should daily be engaged with God’s Word and carry it in our hearts and upon our lips [Psalm 119:11–13]. But as said above, since we do not always have free time, we must devote several hours a week for the sake of the young, or at least a day for the sake of the entire multitude, to being concerned about this alone. We must especially teach the use of the Ten Commandments, the Creed, and the Lord’s Prayer, and so direct our whole life and being according to God’s Word. 90 At whatever time, then, this is being observed and practiced, there a true holy day is being kept. Other things shall not be called a Christians’ holy day. For, indeed, non-Christians can also stop working and be idle, just as the entire swarm of our Church workers do. They stand daily in the churches, singing and ringing bells, but they do not keep a holy day in true holiness, because they do not preach or use God’s Word but teach and live contrary to it.
91 God’s Word is the true “holy thing” [Heiligtum; relic] above all holy things. Yes, it is the only one we Christians know and have. Though we had the bones of all the saints or all holy and consecrated garments upon a heap, still that would not help us at all. All that stuff is a dead thing that can sanctify no one. But God’s Word is the treasure that sanctifies everything [1 Timothy 4:5]. By the Word even all the saints themselves were sanctified [1 Corinthians 6:11]. 92 Whenever God’s Word is taught, preached, heard, read, or meditated upon, then the person, day, and work are sanctified. This is not because of the outward work, but because of the Word, which makes saints of us all. Therefore, I constantly say that all our life and work must be guided by God’s Word, if it is to be God-pleasing or holy. Where this is done, this commandment is in force and being fulfilled.
93 On the contrary, any observance or work that is practiced without God’s Word is unholy before God. This is true no matter how brilliantly a work may shine, even though it is covered with relics, such as the fictitious spiritual orders, which know nothing about God’s Word and seek holiness in their own works.
94 Note, therefore, that the force and power of this commandment lies not in the resting, but in the sanctifying, so that a special holy exercise belongs to this day. For other works and occupations are not properly called holy exercises, unless the person is holy first. But here a work is to be done by which a person is himself made holy. This is done (as we have heard) only through God’s Word. For this reason, particular places, times, persons, and the entire outward order of worship have been created and appointed, so that there may be order in public practice [1 Corinthians 14:40].
95 So much depends upon God’s Word. Without it, no holy day can be sanctified. Therefore, we must know that God insists upon a strict observance of this commandment and will punish all who despise His Word and are not willing to hear and learn it, especially at the time appointed for the purpose.
96 It is not only the people who greatly misuse and desecrate the holy day who sin against this commandment (those who neglect to hear God’s Word because of their greed or frivolity or lie in taverns and are dead drunk like swine). But even that other crowd sins. They listen to God’s Word like it was any other trifle and only come to preaching because of custom. They go away again, and at the end of the year they know as little of God’s Word as at the beginning. 97 Up to this point the opinion prevailed that you had properly hallowed Sunday when you had heard a Mass or the Gospel read. But no one cared for God’s Word, and no one taught it. Now that we have God’s Word, we fail to correct the abuse. We allow ourselves to be preached to and admonished, but we do not listen seriously and carefully.
98 Know, therefore, that you must be concerned not only about hearing, but also about learning and retaining God’s Word in memory. Do not think that this is optional for you or of no great importance. Think that it is God’s commandment, who will require an account from you [Romans 14:12] about how you have heard, learned, and honored His Word.
99 Likewise, those fussy spirits are to be rebuked who, after they have heard a sermon or two, find hearing more sermons to be tedious and dull. They think that they know all that well enough and need no more instruction. For that is exactly the sin that was previously counted among mortal sins and is called akadia (i.e., apathy or satisfaction). This is a malignant, dangerous plague with which the devil bewitches and deceives the hearts of many so that he may surprise us and secretly take God’s Word from us [Matthew 13:19].
100 Let me tell you this, even though you know God’s Word perfectly and are already a master in all things: you are daily in the devil’s kingdom [Colossians 1:13–14]. He ceases neither day nor night to sneak up on you and to kindle in your heart unbelief and wicked thoughts against these three commandments and all the commandments. Therefore, you must always have God’s Word in your heart, upon your lips, and in your ears. But where the heart is idle and the Word does not make a sound, the devil breaks in and has done the damage before we are aware [Matthew 13:24–30]. 101 On the other hand, the Word is so effective that whenever it is seriously contemplated, heard, and used, it is bound never to be without fruit [Isaiah 55:11; Mark 4:20]. It always awakens new understanding, pleasure, and devoutness and produces a pure heart and pure thoughts [Philippians 4:8]. For these words are not lazy or dead, but are creative, living words [Hebrews 4:12]. 102 And even though no other interest or necessity moves us, this truth ought to urge everyone to the Word, because thereby the devil is put to flight and driven away [James 4:7]. Besides, this commandment is fulfilled and this exercise in the Word is more pleasing to God than any work of hypocrisy, however brilliant.