By Jesse Morrell
http://www.OpenAirOutreach.com
This was a post I made in my Facebook theology discussion group: https://www.facebook.com/groups/TheologyDiscussionGroup/
I wrote:
Even apart from the scriptures that teach such, the doctrine that salvation can be forfeited through sin is a logical conclusion of the necessity of repentance from sin as a precondition for forgiveness.
If it is granted that repenting of your sin is a precondition of forgiveness for that sin, then it stands to reason that a believer who returns to his sin is unforgiven until he repents. Thus, a believer can forfeit his salvation through sin (like the unforgiving servant did).
The Calvinist system seems to be inconsistent on this point. They will admit that repentance is necessary for unbelievers to be forgiven but deny that a believer who sins is unforgiven until he repents. They teach that to initially get saved an unbeliever must repent, but if a believer sins he will repent (perseverance of the saints) yet was still saved while he was sinning and impenitent.
Can any Calvinists in this group enlighten me on this issue?
I wonder if this is why some Calvinists become straight up antinomians, teaching that you do not need to repent of your sins at all and classify that as “works based salvation” or “salvation by works,” because logically repentance as a precondition for forgiveness means that you can lose your salvation through sin and impenitence and thus need to live a holy and obedient life as a condition of keeping your salvation.
So to be consistent, it would seem to me, that Calvinists must either adopt the Arminian doctrine of losing your salvation or reject repentance from sin all together and become Antinomians.
Biblical Truth Resources 
Since the scriptures teach repentance is a precondition of forgiveness, a sin is unforgiven until it is repented from. When this truth is consistently held, the doctrine of the possibility of forfieting salvation cannot be logically denied, if it is affirmed that it’s possible for believers to sin. A person must repent of their sin to get saved and must stay away from sin to stay saved. A believer who sins is consequently a backslider who must repent again for a fresh forgiveness. All of this cannot be avoided if it is affirmed, as the Bible teaches, that repentance must come before forgiveness.
The story in Acts 8 teaches us from important truths:
1. Simon the sorcerer became a believer (Act 8:13)
2. After becoming a believer, he sinned (Act 8:22).
3. For his sinning he was in danger of perishing (Act 8:20).
4. He then needed to repent of his sin to be forgiven (Act 8:22).
From this story we can see that:
1. It is not impossible for a believer to sin. Sinning does not mean that they were never saved to begin with or that they were never a true believer.
2. A believer, through sin, can perish.
3. A believer who sins needs to repent in order to be forgiven. Their present and future sins are evidently not forgiven already.
Examples of believers who lost their salvation through their sin would be Judas (Acts 1:25), Simeon (Acts 8:13-22), the unforgiving servant (Matt. 18:23-35), the unfaithful servant (Luke 12:45-46), the man that abides not in Christ (John 15:6), Hymenaeus and Alexander (1 Tim. 1:19-20), the backslider (Luke 8:12), etc. Peter is an example of someone who backslide into sin and lost his salvation but had it restored by being re-converted (Matt. 10:33; Matt. 26:70-72; Luke 22:32). The Bible does talk about one being restored who had fallen away (James 5:20).
Good post / thoughts from Jesse Morrell.. It also touches on why there are so few white-haired Calvinists. {[ I was in and a member of a Calvinistic church for over 10 years and know whereof I speak. ]}
Logically , if you follow the Calvinistic / Reformed writers and authors of Theology books , and Professors and now – the internet posters/bloggers , you really have NO reason to even try and live a holy life. IF everything has already been pre-programed for all humans… may as well stay at home on the Lord’s Day and watch football games and not even bother to do any of the things mentioned in the Bible for a believer to do in this life.
Several Calvinists start being Calvinists in their late 20’s to mid 30’s — it seems like a logical religion , and it has lots of “answers” —– But by the time when they should be Elders and or deacons ( in their 50’s and 60’s ) ,,, they have left the flock and are either playing computer games or have turned into functional atheists.