The Sunday Sermon

The Ten Commandments Part 2a
By Martin Luther

Thou shalt not take the name of the Lord, thy God, in vain.
Exodus 20:7

As the First Commandment (Exodus 20:3) has instructed the heart and taught the basis of faith, so this commandment leads us forth and directs the mouth and tongue to God. (Isaiah 45;23) For the first objects that spring from the heart (Matthew 15:19; Proverbs 4:23) and manifest themselves are words. (Matthew 15:11, 18) Now, as I have taught above how to answer the question, what it is to have a god, so you must learn to comprehend simply the meaning of this and all the commandments, and to apply it to yourself.
If, then, it be asked: How do you understand the Second Commandment, or what is meant by taking in vain, or misusing God's name? answer briefly thus: It is misusing God's name when we call upon the Lord God no matter in what way, for purposes of falsehood or wrong of any kind. Therefore this commandment enjoins this much, that God's name must not be appealed to falsely, or taken upon the lips while the heart knows well enough, or should know, differently; as among those who take oaths in court, where one side lies against the other. For God's name cannot be misused worse than for the support of falsehood and deceit. Let this remain the exact and simplest meaning of this commandment. (Exodus 20:16; Exodus 23:1)
From this every one can readily infer when and in how many ways God's name is misused, although it is impossible to enumerate all its misuses. Yet, to tell it in a few words, all misuse of the divine name occurs, first, in worldly business and in matters which concern money, possessions, honor, whether it be publicly in court, in the market, or wherever else men make false oaths in God's name, or pledge their souls in any matter. And this is especially prevalent in marriage affairs where two go and secretly betroth themselves to one another, and afterward abjure their plighted troth.
But. the greatest abuse occurs in spiritual matters, which pertain to the conscience, when false preachers rise up and offer their Lying vanities as God's Word. ( Mark 13:22; 2 Peter 2:1 Matthew 7:15; Matthew 24:11)
  Behold, all this is decking one's self out with God's name, or making a pretty show, (Matthew 23:5) or claiming to be right, whether it occur in gross, worldly business or in sublime, subtile matters of faith and doctrine. And among liars belong also blasphemers, not alone the very gross, well known to every one, who disgrace God's name without fear (these are not for us, but for the hangman to discipline); but also those who publicly traduce the truth and God's Word and consign it to the devil. Of this there is no need now to speak further.
Here, then, let us learn and take to heart the great importance of this commandment, that with all diligence we may guard against and dread every misuse of the holy name ( James 3:5, 8), as the greatest sin that can be outwardly committed. For to lie and deceive is in itself a great sin, but is greatly aggravated when we attempt to justify it, and seek to confirm it by invoking the name of God and using it as a cloak for shame (Ephesians 4:17-19; 1 Peter 2:16), so that from a single lie a double lie, nay, manifold lies, result.