"... a man is not justified by the works of the law..." Many Christians thinks this scripture means that works are no longer necessary after being saved.
"Stand fast therefore in the liberty..." Many Christians think this scripture means that we need to stand fast in our liberty of not being very religious. "Grace is enough" is their mantra. They smirk at the devout Christian.
"...he might trust in the flesh, I more..." Many Christians think Paul is boasting in his sin or weaknesses and confessing that sin is a hopeless condition until Christ returns.