One verse that is particularly popular with heretics who claim salvation involves works is Philippians 2:12, which says "Wherefore, my beloved, as ye have always obeyed, not as in my presence only, but now much more in my absence, work out your own salvation with fear and trembling." The conclusion that is erroneously drawn from this verse is that if you don't work for your salvation, you lose it.
A very obvious flaw in this interpretation is that Paul does not say work for your own salvation with fear and trembling, but rather, work out your own salvation with fear and trembling. As far as I am aware, no translation, including corrupt translations, render this verse "work for your own salvation". The reason it doesn't say that is because it doesn't mean that. Indeed, even the word "fear" here doesn't mean what people think it does, as is shown by 1 John 4:18, which says "There is no fear in love; but perfect love casteth out fear: because fear hath torment. He that feareth is not made perfect in love." Evidently, Paul is not telling the Philippians "be imperfect in love, or you'll go to Hell".
So what is the correct interpretation? With regard to fear and trembling, this refers not to constant worry that one might lose salvation, but rather, granting the Lord the respect He deserves. God is not a joke, nor is His salvation a toy. We who have been saved ought to be in such awe of God that we constantly think about Him, meditate on His words, and, of course, "work out" our salvation. But what does that mean?
Quite simply, it means that though we have salvation, it has not yet reached its completion. No one converts and then instantly becomes Jesus. Yet, the final goal of our salvation is not even to merely inherit a place in His Kingdom. No, we are supposed to be like Him. In this life, this seems unattainable. We are weak in the flesh, and the desires of that flesh constantly wars against the desires of the spirit. If we are saved, we must seek to win that war. And how do you win a war? With strength. If you don't work out your salvation, you stop acting saved. You become less effective in your walk with Christ, be it in your Church life, in your witness, in your personal life, or anywhere else you're not working out.
One way in which we fear God is to recognise the value of His word. That includes its internal consistency. God does not speak with a forked tongue, nor is He double-minded. He means what He says, and says what He means. His Apostles, flawed though they were, did likewise when they, guided by His Holy Spirit, wrote His Scriptures. It is worth noting, therefore, that the same Paul who told the Philippians "work out your own salvation with fear and trembling" told the Ephesians "by grace you are saved through faith, (...) not of works" (see Ephesians 2:8-10). Therefore, if we are to work out our salvation with fear and trembling, it is vital to recognise exactly how it is obtained. That is, we understand that we do not work for our own salvation. Rather, Jesus worked for our salvation, as indeed we never could. We, therefore, receive salvation as a beautiful gift from God. We therefore strive hard in our faith, seeking to imitate Christ as best we can, until the day that goal is finally complete, be it by our death or rapture. While on earth, we will fail constantly, not to the loss of our salvation, but to its disgrace. This disgrace is a great tragedy, and ought to be fought against with great valor. This is what it means to work out our salvation.