Galatians 5:4 Christ is become of no effect unto you, whosoever of you are justified by the law; ye are fallen from grace.
Only difference is that they haven’t fallen from grace because they believed right from the start that they are justified by the Law.
In other words, they don’t believe that they are justified FREELY by His grace :
Romans 3:24 Being justified freely by his grace through the redemption that is in Christ Jesus:
Romans 11:6 And if by grace, then is it no more of works: otherwise grace is no more grace. But if it be of works, then it is no more grace: otherwise work is no more work.
But if it be of works, then it is no more grace…….