I'm not against believing that losing salvation is extremely difficult but I can't see how it is impossible. For example the verse
“Not everyone who says to Me, ‘Lord, Lord,’ shall enter the kingdom of heaven, but he who does the will of My Father in heaven. Many will say to Me in that day, ‘Lord, Lord, have we not prophesied in Your name, cast out demons in Your name, and done many wonders in Your name? . And then I will declare to them, ‘I never knew you; depart from Me, you who practice lawlessness!’ (Matthew 7:21)
This is a pretty strong verse leaning towards being able to lose salvation. There is no unbeliever that would be casting out demons in Jesus name, or prophesying in His name, doing wonderful works. These were serious Christians. They were actually fullyfilling what Jesus commanded. To heal the sick, cast out demons, prophecy, speak in new tongues. Most Christians today aren't doing these things. So it isn't a question of whether they were Christians or not, but rather what exactly expelled them from the presence of the Lord. It is the practicing of lawlessness that destroyed their right standing with the Lord.
“He who overcomes shall be clothed in white garments, and I will not BLOT OUT his name from the Book of Life; but I will confess his name before My Father and before His angels.” (Revelation 3:5)
This also states a born again believer for those who believe that once you are born again your name is written in the Lambs book of Life. It is true that it can never be erased, but it can be blotted out as Jesus says in revelation. This states that you must be an overcomer to the very end, not start off great and the fizzle out towards the end.
English Standard Version (©2001)
and by which you are being saved, if you hold fast to the word I preached to you—unless you believed in vain.
This translation express being saved, as in a continual thing, but also conditional by the fact that you must hold fast the words of God. It would be vein to start of with Christ and you let circumstances destroy your faith to the point where you don't look to Christ anymore. This was written to the Corinthians who were on some very shaky ground in their walks with Christ.
Hebrews 6:4-6 states, “For it is impossible for those who were once enlightened, and have tasted the heavenly gift, and have become partakers of the Holy Spirit, and have tasted the good word of God and the powers of the age to come, if they fall away, to renew them again to repentance, since they crucify again for themselves the Son of God, and put Him to an open shame.”
Finally their are actually 2 ways to disqualify yourself from heaven. One is the unpardonable sin, which is blatently denying Christ. Which is done by an unbeliever and possibly by a believer. The other is called the "sin unto death". Which isn't a specific sin, but 5 criteria a believer has to meet to have committed. Paul says when you are praying for a backslider and God reveals they have committed the sin unto death, that you are to pray for them no more.
The funny thing about this sin is it has nothing to do with unbelief, but rebellion. But if you read carefully this is a sin committed by very mature Christians(once englightened, tasted of the heavenly gift, partakers of the Holy Spirit, tasted the good word of God, and powers of the age to come), ones that have been saved, spirit-filled, have been given some sort of unique gift, very deeply Biblically knowledgable, and have drank deep of the things of God. And this person has to commit a vile act against Christ. Where he would bring Christ to an open shame, and crucify Him once again in their hearts. A famous preacher who has preached to millions of people, said that only 2 times in his life did God tell him to quit praying for someone because of this sin. He was very adament about praying for backsliders.
My own Pastor talks about former church members and leaders that have back slidden from God. And he has gone to the hospital in their last moments of life, and they are cursing God as they enter into eternity. These weren't flaky Christians, these were leaders and many who led other to Christ and build church foundations. But the enemy was able to deceive them to believe a lie.
"trodden under foot the Son of God", have counted the blood of the Son of God, "the blood of the covenant", an unholy thing, and have "done despite unto the Spirit of grace"
Again I believe every soul on earth has the ability to be saved, this much is clear. I also believe it is very difficult to lose salvation once you have become a child of God. But I wouldn't venture to say it is impossible, their is just to much evidence to the contrary.