Romans 10:13
For whosoever shall call upon the name of the Lord shall be saved.
Is a TRUE statement. God cannot lie so His word stands firm.
Everybody who walks up the alter and calls upon the name of Jesus is saved. But they are not OSAS.
A prostitute who walks into your church and is convicted of her sins by the Word of God and walks up to alter and calls upon the name of Jesus and is saved. She is a Born again member of the family of God.
You then teach her that she is OSAS right afterwards. I have seen this done. She returns home to the real World and is a sheep amongst the wolves. She falls back into her lifestyle because she is weak. She believes she is OSAS because she was taught this. It's the only thing she remembers after a while. It is this concept that allows her to continue in the lifestyle. If she wasn't taught this concept the Holy Spirit could convict her of her sins and she would get out of it. But why should she? She is OSAS!
A false doctrine has her trapped in a life of sin. Over time she Hardens her heart further because of sin and crosses the line into Apostasy. Maybe she converts to Islam? She is now lost and will be cast into the fire.
OSAS only applies to those who ends up in Heaven.
The verse "For whosoever shall call upon the name of the Lord shall be saved." stands as a truth because it doesn't say
For whosoever shall call upon the name of the Lord shall be saved forever no matter what they do!