Once Saved Always Saved Part VIII b

Broadly speaking, there are two types of verses that warn the Christian against losing their salvation:

1. Verses which look like they teach it, but on closer examination, don't. In the end these only serve to strengthen the idea of eternal security.
2.  Verses which do teach that faith can be lost, and that some people will fail to persevere until the end. Far from tearing the doctrine down, these verses help clarify and sharpen our idea of it.

In this post we'll look at the first category, the commonly cited verses that don't actually interact with Once Saved Always Saved. In the next post we'll look at those that do.
In both cases we'll find Scripture doesn't contradict itself, cannot be broken, and harmonize just fine with what we now know to be true.

Hebrews 6:4-6

It is impossible for those who have once been enlightened, who have tasted the heavenly gift, who have shared in the Holy Spirit, who have tasted the goodness of the word of God and the powers of the coming age, if they fall away, to be brought back to repentance, because to their loss they are crucifying the Son of God all over again and subjecting him to public disgrace. 

This is perhaps the most common verse appealed to to argue that a true believer can lose their salvation, and also the most amusing one, since it effectively robs Peter to pay Paul.
First, for this argument to work the person being discussed must be an elect believer. If he is merely professing faith with an unregenerate heart then he remains unsaved all along and the difficulty is resolved. All the man is doing by coming near to Christ is tasting it, realizing it doesn't sit well with his digestion, and rejecting it. Such a man has rejected the only hope for eternal life and therefore cannot be saved. Personally I think this interpretation has a lot going for it and makes perfect sense of the text.
But let's assume it doesn't and the verses are speaking of the elect. In that case if the believer falls away it is impossible that he can come back, which contradicts Romans 11 which states that "if they do not continue in unbelief they will be grafted back on." Is the person who raises an objection to Once Saved Always Saved really willing to say that those who fall away even a single time are doomed forever? Not that I've ever seen.
So it must be speaking hypothetically. If an elect believer were to fall away, then he's trampled on the blood of Christ and made it completely unusable to save. If an elect person can do the impossible of getting lost in the face of God's saving power then it's going to make getting found again impossible too. So the passage is not arguing that falling away is possible, but instead that such a position is illogical and absurd. Far from threatening believers, it's a comfort to them.

Matthew 6:15 

"But if you do not forgive others their trespasses, neither will your Father forgive your trespasses."

In this portion of Scripture we learn that unless a person adopts a forgiving posture they won't be forgiven themselves, which speak to the conditions for salvation, not the nature of it. It teaches us that one of the requirements for salvation is a spirit of forgiveness (which really just turns out to be a new, living, un-stony heart). The point is that regeneration is necessary for salvation.
For this verse to contradict eternal security it would have to say something like: God will not forgive the sins of some of the elect because some of them are a cruel and unforgiving bunch. But it doesn't. It doesn't say the elect won't adopt that posture, and in this way adds to our understanding of who the elect are by informing us they're forgiving people. The verse actually isn't threatening them at all.
In the same vein, we might add Matt 5:22, 29; 10:28; 18:9, 35 with the same answer.

Revelation 2:10 

"Be faithful unto death, and I will give you the crown of life."

This passage is a promise of Christ to reward His people to stand strong because He has something better for them than what they're giving up. To take its intended meaning of hope and encouragement and change it into a warning that people are likely to lose their salvation unless they work for it is frankly, cruel and unfaithful to the text.
The reason it seems to back into a warning is straightforward: those who have died in Christ are not in the same position as those who are still living. There's a difference between the faithful living and faithful dead in that the living Christian operates by faith in the promises while the sleeping one does so by sight. Eternal security means the crown belongs to the saint, he cannot lose it, it is waiting for him, it is only a matter of time, it does not mean however, that he's wearing it.

Galatians 5:3

"You who are trying to be justified by the law have been alienated from Christ; you have fallen away from grace."

The church in Galatia had been taken over by legalists who traded salvation by grace for salvation by works by mixing in circumcision and law keeping to Christ's perfect atonement. And since salvation is either by grace through faith or not at all, the result was that these people were therefore no longer saved.
Before I go further let me point out the irony of someone who believes in keeping their salvation by their own effort appealing to a passage which teaches salvation is all of grace in an attempt to prove it can be lost. That's just too good to miss. The weapon disintegrates in their hands before they can use it.
That aside, this is another factual statement about salvation: if you are trying to be declared as righteous by works the law you are not going to be save by grace through faith. If you were in a state of salvation before, then you're not now.
But it is true that faith can be lost. So let's come to those verses now.

Next: Part VIIIc - The Faithful Persevere