At this point, when I read what someone writes attacking eternal security, I don't hear anything new. I wouldn't mind hearing something new. I wouldn't mind hearing something of a supportive nature for eternal security. Either way, it hasn't happened for awhile. It still hasn't after reading someone who's been arguing against eternal security at a fundamentalist website (SharperIron). After a tremendous amount of interaction from both sides of the issue, I kind of understand how someone might be confused. It's not because the Bible isn't clear. It's plain. However, if you looked at certain verses not in both their immediate or a larger context, they might seem like the Bible is actually teaching conditional security.
What anyone reading needs to recognize is that since God is one, He won't contradict Himself. All of the doctrine of the Bible fits together. If the Bible teaches eternal security in one or several places, then it won't be contradicted in other places. All the various passages harmonize with one another.
On the other hand, there is often a razor-thin balance between certain doctrines. They're almost seamless. They don't contradict, but there is little room between them. Here's what I mean on this particular subject. If God says, once you believe in Christ, you're saved forever, can never lose the salvation, someone might think that he could live any way he wanted after that. He can't. Even better, he won't. Why? People who don't live for the Lord won't be saved. They aren't saved. If they say they've believed in Jesus Christ, that's possible, but it's a dead faith. Saving faith changes someone's life. He is a new creature. So do you get saved by living for the Lord? No. But you will live for the Lord if you're saved. The one who lives for the Lord will be saved. There is a fine line, like I mentioned. But there is a line.
If someone makes a profession of faith and then doesn't keep living the Christian life, did he lose his salvation? No. Salvation is of the Lord. God is the one doing the saving. And once He saves, He keeps saving. There can only be one explanation, and it is made in Scripture. He was never saved in the first place. There are two places that make this point: 1 John 2:19 and 1 John 3:6.
They went out from us, but they were not of us; for if they had been of us, they would no doubt have continued with us: but they went out, that they might be made manifest that they were not all of us.
Whosoever abideth in him sinneth not: whosoever sinneth hath not seen him, neither known him.
In the first verse, notice it says, "If they had been of us, they would not doubt have continued with us." Anyone who is really saved will continue. He will persevere. He will overcome. And then look at the next part: "They went out, that they might be made manifest that they were not all of us." When someone "falls away" or "turns away," he is just manifesting that he never had it in the first place. He "went out," because he was not "of us," not because he lost anything.
The second verse explains why someone lives a lifestyle of sin, goes about in habitual sinning (present tense verbs). The reason someone won't live the Christian life is because he has "not seen him, neither known him." The assumption you should have is that if he had seen Christ and known Christ, he would not be living a lifestyle of sin. In other words, if he were saved, he would continue in righteousness, not depart from the faith.
Someone might ask, "What is apostasy?" A saved person cannot apostatize. Only an unsaved person can apostatize. Apostasy is when a person experiences salvation in the greatest possible way, yet without actually receiving Christ, and then turns from salvation. Hebrews 6:1-8 describes this. A person interacts with the most revelation he can without receiving it in a saving fashion, and then turns away from it. That is an apostate. That is Judas Iscariot. Apostates are people never saved in the first place.
There are two other aspects that people become confused about. One is the eschatological use of the term "saved." If I say, people who do not live a lifestyle of good works will not be saved, I'm not saying that someone is saved by works. I'm saying that his life is changed through justification and regeneration, and so he will live good works before he is glorified. Glorification is the eschatological salvation. People who will be saved are people who are converted and they do live a Christian life.
The other is the use of conditional sentences. One of these is Colossians 1:22-23:
To present you holy and unblameable and unreproveable in his sight: If ye continue in the faith grounded and settled, and be not moved away from the hope of the gospel.
Those two verses say that you'll be presented holy and unblameable and unreproveable, if ye continue in the faith grounded and settled. Some might say that these two verses teach that you are saved by continuing. They don't say that. People who do not continue are not saved. People who do continue are saved. People who are saved will be presented to God holy and unblameable and unreproveable. Why? They are saved. People who are saved will continue. A side point, that isn't the case with every conditional sentence, but it is true in the above two verses is that the conditional sentence ("if") is a first class condition (ei with the indicative). The first class conditional sentence is a condition of reality or as A. T Robertson says, "Determined as fulfilled." So the condition of "continuing" is determined as fulfilled. The fact that there is a condition ("if") doesn't mean that someone who is saved might not continue in the faith grounded and settled.
How I explain the above situation is that for everything that God does, we cooperate with it. God keeps saving us, so we keep continuing. We act as if our not continuing will result in us not being saved, because that's how God presents it. God is doing all the saving, but if He is doing that, we are cooperating with it. We have to cooperate with it, but we will because God is doing the saving.
Much more can be said about this, but what's the danger in thinking that we've got to do works in order to stay saved? It's all presented in Galatians 5:1-4. Any work added to grace nullifies grace. Christ is become of no effect unto the person. He becomes a debtor to do the whole law. Christ profits him nothing. Anyone who says he must keep living obediently or lose his justification has added works to grace. It's ironic. He thinks that he will apostatize by stopping the doing of good works, but instead he's apostatized by adding works to grace.