The doctrine of OSAS acknowledges that the unbeliever can choose to continue in unbelief and go to an eternal hell. Or, the unbeliever can choose to believe in Jesus Christ and go to heaven for all eternity.
This is correct.
But OSAS teaches that once a person has at a point in time believed in Jesus Christ, then that person loses their choice to reject Jesus. Thus the true believer in Jesus Christ has no option to go to hell for all of eternity. Even if this person swears and yells and screams at God and says he does not want to be in heaven with an all-loving Father: this person has no choice or option to back out of what happened at his new birth - he is going to heaven whether he wants to or not.
And this is the point. When a person truly becomes born again (from above), having become a new creature (creation), they belong to God. He
owns us,
bought and paid for with the
precious blood of Jesus. A true child of God cannot be un-born again, and he certainly cannot make any decisions about that with which he no longer has
rights. He cannot sell himself back to the devil (or sin, or however you want to say it) because he doesn't
own himself anymore. God does. Only God
could, but He
will not because He paid such a high price, and now that He
owns the purchased possession, He will keep it and protect it forever. The decision to trust Christ is a one-time only decision, and if truly heart-felt (sincere, genuine), then it is forever.
Like I said before, the child of God has
already made the decision (which once made, cannot be un-done).