Then God made a mistake, and gave you something he called free, and then because you did not earn it. Took it away,
You can not give a gift back, it is still yours, You may fail to be blessed by the gift, because it is not in your hands and your not using it, but it is still yours. The owner does not take it back.
The warning are not for believers. They are for non believers who are in the church who have not yet taken that step,. Paul and John both speak about how we are not the ones who fall to perdition, we are not the ones who walk away, we are not the ones who need to be taught,
You never assume each person in your body are true believers, you must always give a warning to all, even though the few are the ones who need to hear it, because you may not know who they are.