Are you serious? Make you case for OSAS. Show me a single passage that says salvation can't be lost. I can show plenty that say it can. You claim it's a doctrine that can't be challenged yet not only can it be challenged, it can't even be found in Scripture. The best argument that the OSAS side can present it one from inference. It has to be inferred because there is "NOT" a single passage of Scripture that states it. One would think a doctrine of such magnitude would have a least a single passage of Scripture to support it, yet OSAS has nothing. Since it isn't stated it can't be proven, thus it's an opinion.
As I said, the doctrine has it's roots in Gnosticism and Greek Philosophy. Here's Origen refuting the idea of OSAS around 285 A.D.
8. Let us begin, then, with what is said about Pharaoh—that he was hardened by God, that he might not send away the people; along with which will be examined also the statement of the apostle, “Therefore hath He mercy on whom He will have mercy, and whom He will He hardeneth.” And certain of those who hold different opinions misuse these passages, themselves also almost destroying free-will by introducing ruined natures incapable of salvation, and others saved which it is impossible can be lost; and Pharaoh, they say, as being of a ruined nature, is therefore hardened by God, who has mercy upon the spiritual, but hardens the earthly.
Early Church Fathers - – Ante-Nicene Fathers:
Well like I said these are all RCC sources and of course they agree with RCC doctrine. Like I said you have no information that confronts reformation doctrine but that which was the object to be protested and reformed.
And many scriptures that prove this doctrine have been presented to you. It requires faith to have confidence in the promises of God. If one does not have faith, of course they will not believe what the promise says.
Now I have quoted ONE scripture and it in itself proves my point that NOTHING CAN seperate a believer from the love of God. If that does not save one forever? Then I do not know what does?
Rom 8:38-39
I am not here to defend OSAS, nor is there one constant doctrine that those who use the term all agree too.
But in general, it is a sound and very biblical position.
Now Origen himself was accused by many of being a heritic,
and his teachings are NOT ACCEPTED as any witness to the truth of scripture.
The insult you charge against those who believe the clear and evident truth of the scriptures, is just that? an insult and it has no purpose other than to make a false charge against the true gospel.
