15 These {Ten Commandments, Apostles’ Creed and Lord’s Prayer} are the most necessary arts of Christian instruction. We should learn to repeat them word for word. 16 Our children should be taught the habit of reciting them daily when they rise in the morning, when they go to their meals, and they go to bed at night; until they repeat them they should not be given anything to eat or drink. 17 Every father has the same duty to his household; he should dismiss man-servants and maid-servants if they do not know these things and are unwilling to learn them. 18 Under no circumstances should a person be tolerated if he is so rude and unruly that he refuses to learn these three parts in which everything contained in Scripture is comprehended in short, plain, and simple terms, 19 for the dear fathers or apostles, whoever they were, have thus summed up the doctrine, life, wisdom, and learning which constitute the Christian’s conversation, conduct and concern.
20 When these three parts are understood, we ought also to know what to say about the sacraments which Christ himself instituted. Baptism and the holy Body and Blood of Christ, according to the texts of Matthew and Mark at the end of their Gospels where they describe how Christ said farewell to his disciples and sent them forth. (Shorter Preface of Large Catechism -Tappert, p. 363-364).