First, I don't like the term "Once Saved Always Saved". I prefer the phrase "Perseverance of the Holy Spirit".
The phrase "Once Saved Always Saved" conveys the idea of "easy believism"; that someone can be saved, and go off and never care a whit for God and works of appreciation and love for Him. This term is more of a slander to monergists in my opinion, although I believe that anyone who is really saved will never lose that salvation. But, true faith produces works, as James said. The works are not to earn or merit salvation, though, they are done out of appreciation and love for God...not in slavish fear like those who try to deny eternal security possess.
A saved individual can backslide, even for long periods of time, but the Lord will chasten him and bring back the errant sheep into the fold, no matter what it takes. If someone leaves a profession of faith, and never returns, this is proof that they never possessed the faith....they only had a false profession of faith. Scriptures are consistent with this view.
I view this issue of eternal security to be one of maturity. Immature believers really don't understand the full nature of the grace of God and his unending love for those he's saved. So while a person can be saved and have a works oriented salvation, like I believe most who deny eternal security have, they are still saved. They are a bit like a man who goes on a cruise, and fills his luggage with cheese and peanut butter and crackers....unaware of the smorgasbord that is included in the price of the cruise...instead he stays in his small room and eats inferior food rather than enjoying the good stuff that he should be enjoying.
As a monergist, I believe God is sovereign in all things INCLUDING salvation. If anyone sincerely desires to study this in more depth, I highly recommend this pdf document.
http://www.wholesomewords.org/etexts/ironside/eternal.pdf
Regarding the specific verses that the thread originator posts, I will refer you to the PDF document but am producing the section that covers this verse here. Read this carefully and think about what it's saying. Realize that there was a difference in the covenant that God had with ancient Israel, which was one of works/law and material/national promises, and the one that he has with Christians, which is one of faith/grace and spiritual/individual promises. This is the difference between what it means to be an Israelite and a Christian. Some in the Old Testament had a real relationship with God based on faith, such as Abraham, Isaac, Jacob, Moses, David, the prophets....however as the Old Testament clearly teaches, the nation of Israel as a whole didn't have that sort of relationship and never followed God wholeheartedly.
Q. Ezekiel 18: 24: "But when the righteous turneth away from his righteousness, and committeth iniquity, and doth according to all the abominations that the wicked man doeth, shall he live?"
A. Is it not strange for anyone in this dispensation of grace to quote a passage like that, as though it had anything to do with the question of the soul's salvation? Go back and read Ezekiel 18. Of what is it treating?
We read in the twenty-first verse, "If the wicked will turn from all his sins that he hath committed, and keep all My statutes, and do that which is lawful and right, he shall surely live, he shall not die." Is that grace? No, that is law.
That is just the quintessence of law. Do you believe that if a wicked man turns from his wickedness he will live?
If this is true, why did Jesus die? Would you preach that to sinners? Would you have me stand up and say, "You wicked people, you have been doing wickedness; you start in tonight to do righteousness and you will live"-would you have me preach that? I would be deliberately deceiving people if I told them that.
But you see here God was testing people under law and said, "The man that turneth away from his righteousness, and committeth iniquity, and doeth according to all the abominations that the wicked man doeth, shall he live?
All his righteousness that he hath done shall not be mentioned in his trespass that he hath trespassed, and in his sin that he hath sinned, in them shall he die."
And what has happened? Not one man ever continued in all the things that are written in the book of the law to do them. Therefore, they were all under sentence of death. How then were they to be saved?
By turning over a new leaf? Oh, no; but by confessing that they had no righteousness. If they had, it would only be filthy rags. But now they find all their righteousness in the Lord Jesus Christ, "who of God is made unto us wisdom, righteousness, sanctification, and redemption."
Do not ever quote Ezekiel 18 as though it were gospel. It is law. And then remember the "life" spoken of in Ezekiel is not eternal life in Christ. It is life here on earth prolonged under the divine government, because of obedience, or cut short because of sin