Commandments four through ten describe relationships with our fellow humans. Here Luther's understanding of "vocation" is apparent. Vocation comes from the Latin vocare, meaning "to call." God calls everyone to certain roles—or stations—in life. In this commandment, Luther describes our duty before God to honor father and mother, that is, to respect authority. God instituted all forms of authority as an extension of parental authority, for our good. There are various parental authorities, or "fathers," in our lives, including pastors, teachers, and government officials. Another insight by Luther is about the life of good works to which Christians are called. We should not regard "Church work" as more holy than the other things in life that we routinely do. Rather, all callings and stations in life serve God and are are opportunities for us to obey God's commandments and to serve our neighbor. The key observation Luther offers is this: faith is what makes a person holy. Faith alone. Good works serve God by serving other people.
In his Large Catechism, Luther begins by defining "holy day" and by explaining how by Christ's time the true understanding of the Sabbath had been corrupted. Because the Third Commandment describes Jewish practice int eh Old Testament, Luther plainly states that the external form of this law does not apply to Christians in the New Testament. It is an error to say that Sunday is the New Testament Sabbath. However, the internal form of this command still applies to Christians today. Christians should regularly devote themselves to a day when they can hear and learn God's Word, so that they do not despise it. For this reason Luther commends worship on Sunday for the sake of good order. In this sense, every day for the Christian should be a "holy day" consecrated by God's Word. Luther presents a clever play on words when he suggests there is only one "holy thing." The German word for "holy things" (Heiligtum) was often used to refer to relics, items believed to have belonged to the apostles and other saints. Yet Luther says the only true "holy thing" is God's Word, which consecrates all things and apart from which nothing we do or say is holy.
The First Commandment instructs our heart toward God. This commandment guides our lips. Using God's name to cover up lies or spread falsehood is a great evil and sin, and it happens in many ways in life. There is no greater sin against the Second Commandment than using God's name to preach, teach, and spread false doctrine. Luther explains how to use God's name properly and how to take an oath without sin. By faith, our hearts and our mouths honor God by confessing Him and His Word purely. Luther recommends beginning and ending each day, and each meal, by making the sign of the cross and commending ourselves to God. Making the sign of the cross is not a "Roman Catholic" practice, but has its roots in the earliest years of the Church. It is a visible way to remind ourselves whose we are through our baptisms and how we have been redeemed by the cross of Jesus Christ.
In the Large Catechism, Luther spends more time on the First Commandment than on any other portion of the Catechism, explaining how essential it is to know, trust, and believe in the true God and to let nothing take His place. He was convinced that where this commandment was being kept, all other commandments would follow. A right relationship with God produces right relationships with fellow human beings.
Dr. Luther never intended the Small and Large Catechisms to be only “church books,” but rather “house books”—to be used in everyone’s homes. In fact, Luther suggests that those who do not know the Ten Commandments, the Creed, and the Lord’s Prayer by heart should not receive the Lord’s Supper. He provides the texts of the Large Catechism as the most necessary parts of Christian doctrine, which should be learned until they can be repeated, word for word, by heart, from memory. Luther was always concerned that, in their preaching and teaching, pastors should speak and teach in a very clear, simple, easily understood way so that people would remember what was preached or taught.