You're exhorted to stand firm, and warned to be careful lest you fall.
Which means, these warnings are not all hot air. They are dead serious. If you don't stand firm in this Faith in Christ, which makes you free, you could fall back into slavery. Paul says that.
He also says that if you go back to living in the sins he listed, you will not be saved.
An exhortation to "Stand firm" inescapably addresses the possibility you might NOT stand firm -- and then fall out of the Faith ---
I don't see anyplace where it says "Stand firm --- or not, it doesn't matter, because you were saved when you were twelve and so you you're saved no matter what you do. Idolatry, sodomy, witchcraft: live that way, it doesn't matter.
So, hey, whether you stand firm or not, bro, it's no biggie. Please ignore my warning to the brothers and sisters in Galatia about all those filthy sins and that "those who live like this will not inherit the kingdom of God."
Yet the Word tells us were sealed by the Spirit and that He will never fail us nor forsake us.
Indeed!
Not stand firm in...
Church,
Mary,
Sacraments,
Wafers,
"Fathers",
Apparitions...
(Where's that darn 'mocking' list when I need it?)