The answer is that its failure is not in its source or character. It failed simply because man is what he is. The very essence of man's justification by law is absolute and unvarying conformity. This requires man's perfect knowledge and understanding from the very moment he comes under the law. If he makes one mistake he becomes guilty under the law, and all of his good deeds in the future can never purge that guilt.
Man is incapable of such perfection.
The law cannot justify , because it arouses carnal desires or passions. We must deal with man as he is. Filled with curiosity, the urge to experiment, and the ambition to learn by experience, man is lured to destruction by that which is forbidden. The very commandment intended to restrain all too often incites. The tragic feature is that the penalty is death.