Because the will is either damned by sin or regenerated by God. And He is always right.
And we know this because the Holy Spirit guides our understanding through Scripture.
How does one determine if the believers will has been transformed by the grace of God, if it is subjective?
Men are known to other men by their fruits.
You've heard all this before, Stu. Nothing's changed.
Isn't my knowledge of other men's fruits, subjective? Besides, what does that really mean?