Vain (1500) (eike) has two general meanings, one referring to their being no cause or reason - without purpose, inconsiderately, groundlessly, without cause (see Col 2:18 below). The more common NT meaning (as in the present verse) which refers to being without success or effect, to no avail, to no purpose or in vain (having no real value or failing to achieve a desired result). Ray Stedman comments on in vain noting that ... it is possible to believe in vain. Your faith in Christ can be of such a superficial nature that you accept all the words of the gospel as a kind of an insurance policy against going to hell but you do not let it change anything in you. That is what Paul calls "believing in vain." And it happens all around us. Just this week I heard of a very prominent leader of a church, an elder, a respected man who has been a faithful Christian for a long time, slipped away from what he had held his faith to be, and fell into moral evil in his life. This has raised the question of whether he has believed in vain or not. There can be a mechanical conformity to Christianity that never sees any need for discipline, for Bible study, for prayer or for fellowship. It merely goes for what it can get out of it. That is believing in vain. Jesus said that will not hold up in the tests of life. When the crisis comes it collapses and fails. He said of certain ones like that, "Many will say to me 'did we not do many mighty works in your name?'" But he will say, "I never knew you; depart from me," {cf, Matt 7:22-23}.The test of true faith, of course, is that it cannot quit. It can fail at times, temporarily, but it really cannot quit. Some years ago a young man called me up and said, "I'm tired of being a Christian. I'm fed up with it. I've tried my best and nothing seems to work so I'm going to quit. I just wanted to let you know." I said, "I think it's a good idea. Why don't you do that? Why don't you give it up?" He said, "What do you mean?" "Well," I replied, "you said it. You said you were going to quit, and I think it's a good idea. Why don't you stop trying to be a Christian and go ahead and live the way you like? Pay no attention to the Bible, or the church, or the Word of God, or anything, and just enjoy yourself. Why don't you?" He said "You know I can't do that." I said, "Yes, I do, and I think it is about time you knew it too!" No, the test of true faith is that you cannot quit. (1Corinthians 15:1-4 Of First Importance) TDNT writes that... The basic meaning is “at random,” “with no plan or goal,” “for no objective reason.” It thus comes to mean “without true right,” and the further senses of “in vain,” “moderately” and “simply” have also to be taken into account. (Kittel, G., Friedrich, G., & Bromiley, G. W. Theological Dictionary of the New Testament. Eerdmans) Eike is used only 6 times in the NT... Romans 13:4 (note) for it is a minister of God to you for good. But if you do what is evil, be afraid; for it does not bear the sword for nothing (for no purpose) for it is a minister of God, an avenger who brings wrath upon the one who practices evil. 1Corinthians 15:2 by which also you are saved, if you hold fast the word which I preached to you, unless you believed in vain. Galatians 3:4 Did you suffer so many things in vain-- if indeed it was in vain? Galatians 4:11 I fear for you, that perhaps I have labored over you in vain. Colossians 2:18 (note) Let no one keep defrauding you of your prize by delighting in self-abasement and the worship of the angels, taking his stand on visions he has seen, inflated without cause (no legitimate reason) by his fleshly mind, "Copy and paste the address below into your web browser in order to go to the original page which will allow you to access live links related to the material on this page - these links include Scriptures (which can be read in context), Scripture pop-ups on mouse over, and a variety of related resources such as Bible dictionary articles, commentaries, sermon notes and theological journal articles related to the topic under discussion." http://www.preceptaustin.org/1corinthians_152.htm#vain