Charles H. Spurgeon on Psalms 139:20

Thine enemies take thy name in vain. In every action three things are considerable, —the end, the agent, the work. These three duly weighed, we shall soon see what it is to take God's name in vain.

1. That which hath no end proposed or is done to no end, may truly be said to be done in vain. As the sowing of seed without reaping the fruit, the planting a vineyard without a vintage, or feeding a flock without eating the milk of it. These are labours in vain. So he that taketh the name of God to no end, neither to God's glory, nor the private or public good, taketh it in vain. Cui bono? is a question in all undertakings. If to no good, as good and better not undertaken at all; it is to no end, it is in vain. If a man have well fashioned legs, and they be lame, frustra pulchras habet tibia claudus, the lame man hath them in vain. The chief end, therefore, in taking this name must be, a) The glory of God, otherwise we open our mouths in vain, as it is in Job. God is willing to impart all his blessings to us, and requires nothing of as again but glory, which if we return not, he may say, as David did of Nabal, for whom he had done many good turns, in securing his shepherds and flocks, etc.; and when he desired nothing but a little meat for the young men he denied it: All that I have done for this fellow is in vain; in vain have I kept all he hath. So, God having done so much for us, and expecting nothing but the glory of his name, if we be defective herein, he may well say all that he hath done for us is in vain. b) Next to God's glory is the good of ourselves and others; and so to take God's name without reference to this end, if we neither promote our own good nor the good of others, it is in vain, ex privatione finis, because it wants a right end; therefore Saint Paul rejoiced, having by his preaching laboured for the saving of souls, c) rejoice, saith he, that I have not run in vain, neither laboured in vain.

2. In the agent the heart and soul is to be considered, which in the person acting is the chief mover. If the soul be Rachah, vain and light, as when we take God's name without due advice and reverence, though we propound a right end, yet we take his name in vain. Therefore the wise man advises "not to be rash with our mouth" (Ec 5:2); and the Psalmist professes that his heart was fixed when he praised God (Ps 57:7): the heart ought to be fixed and stablished by a due consideration of God's greatness when we speak of him. This is opposed to rashness, inconstancy, and lightness, such as are in chaff and smoke, which are apt to be carried away with every blast, and such as are so qualified do take God's name in vain.

3. In the work itself may be a twofold vanity, which must be avoided. Firstly, Falsehood. Secondly, Injustice. a) If it be false, then is it also vain, as theirs in Isa 28:15: "We have made a covenant with death, and with hell are we at agreement; when the overflowing scourge shall pass through, it shall not come unto us: for we have made lies our refuge, and under falsehood have we hid ourselves." And this is that actio erroris, work of error, of which Jeremiah speaketh. Vanitas opponitur veritati, vanity is opposed to verity and truth; therefore a thing is said to be vain when it is false or erroneous. "They are vanity, the work of errors", saith the prophet (Jer 10:15); and as there is truth in natural things, so is there a truth in moral things, which if it be wanting, our speech is vain. b) If unjust it is vain too. "If I be wicked, why then labour I in vain?" saith holy Job 9:29; and, "The very hope of unjust men perisheth", saith the wise man (Pr 11:7); and, "They walk in a vain shadow, and disquiet themselves in vain" (Ps 39:6). If justice be wanting in our actions, or truth in our assertions and promises, they are vain; and to use God's name in either is to take his name in vain. So that if either we take the name of God to no end, but make it common, and take it up as a custom till it come to a habit, not for any good end; or if our hearts be not stable or fixed, but light and inconstant when we take it; or if we take it to colour or bolster up any falsehood or any unjust act, we take it in vain, and break the commandment. —Lancelot Andrews.