Personalities are like metals.
They need to be further refined into purer forms and fashioned into useful shapes.
When Prophet Muhammad (peace be upon him) was asked who among people is best, he responded,
“People are like metals (of different qualities), like gold and silver. The best of them before Islam will be the best of them in Islam — if they understand religion.”
So, by implication, the capacity for ethical and moral behavior is a natural endowment, characteristic and inherent in every human in varying degrees and strength levels. Just like unmined metals and minerals, it is there, lying untapped within every human or else only partially recognized and utilized.
This inherent potential only needs to be polished, guided, and developed through an adequate understanding of human nature and its laws as defined by God, in order to bring out and enhance intrinsic human goodness, strengths, and abilities toward noble and worthwhile aims, even in the best of people. Therefore, describing the sole aim of his mission, Prophet Muhammad (peace be upon him) said, “I was only sent to perfect virtuous character traits.” (Musnad Ahmad) That is, by nurturing natural moral behavior to perfection.