An Explanation of Luther's Small Catechism · Martin Luther
TAKING GOD'S NAME IN VAIN:
CONJURE. [Deut. 18:10-12+] This commandment forbids all magic arts, witchcraft, sorcery, pow-wowing, fortune-telling, and all attempts by signs or formulas to discover what God has kept hidden or to attain what He has withheld. If results are obtained by such means, _e.g._, by pow-wowing, that is no justification for their use. [Matt. 16:26] If we desire to obtain help through the use of God's name, we must pray and not conjure. LIE. The eighth commandment forbids lying in general; this commandment forbids lying by God's name. It is broken by those who teach falsehood and error and yet declare that they are teaching God's Word. [Gal. 1:8] DECEIVE BY HIS NAME. This is done by those who assume Christ's name by calling themselves Christians, and yet are hypocrites, and use religion as a cloak. [II Tim. 3:5+, Matt. 15:8] Sins against this Second Commandment are common, but not small sins. God will not hold him guiltless who commits them.
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