Try reading that passage again; I mean, really read it while paying attention to the grammar. It is one of the most powerful passages that tells us that our salvation is secure. The biggest problem that people have while reading that particular passage is that they get caught up in the middle compound preposition of that sentence. Let me show you what I mean.
First I must point out that when it says "if they shall fall away," the "if" is not in the original text or context of that scripture, neither is the "seeing they." The passage should read as follows (I will not add verse numbers so that we can have a better look at the grammar).
For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost, and have tasted the good word of God, and the powers of the world to come, and have fallen away, to crucify the Son of God again for themselves and put him to open shame. |
Now lets take a look at the grammar of this passage. It starts with "For it is impossible" and then the passage picks up with a long compound preposition (of which I highlighted) that distracts the reader from what the writer is trying to convey. Now grammatically, that long compound preposition can be removed to reveal the simple straightforward meaning of the whole sentence: and when the distraction is removed, we are left with the following, clear meaning of the sentence.
For it is impossible to crucify the Son of God again for themselves and put him to open shame. |
We can even go one step further and remove the preposition "for themselves." Once all of the distractions are removed, we are left with the greatest truth. No matter what happens, once we have acknowledged Jesus Christ as the Savior and have accepted the gift of salvation, it is impossible to crucify the Son of God again and put him to open shame.