Many cannot tell the difference between the true Christians and the apostates(pretend believers).
It's not just the world that cannot tell the difference, it's also those that call themselves Christians.
This is why many do not believe in OSAS.
When God gives His child a new heart He doesn't change His mind and say, oh I messed up here's your old heart back.
God doesn't say to His child, oh remember that eternal life, I was just playing with you.
When God says something He truly means it.
No one can snatch my children out of My hands!
My children know Me and I know them.
My children will hear My voice and they will come to Me.
When you become a true child of God you have a new heart and you're in good hands. You have eternal life!
Nowhere in Scripture says that a true child of God will fall away from their faith and lose their salvation.
Apostates will fall from their faith because they truly weren't a child of God in the first place.
Did they lose their salvation?
Of course not, they never had it in the first place.