Man can not attain moral perfection for he is a broken creature from original sin. Christ has shown us through Him moral perfection is possible. Therefore moral perfection is attainable through the Grace of God only.
Being such, to say that we can not attain this when Jesus says all things are possible through Him and it is by His Grace that we can is to try to limit His power. Further, our Mother Mary did attain this by being gratia plena “full of Grace.”
Also being, without Grace we sin and through Grace we are made able to live according to Christ. Thus showing, that Grace allows us to not sin and live in His perfect image, therefore in fullness of Grace there can be no sin just as our Mother Mary had no sin.
This concludes that through the Mediatrix and co-mediatrix that Grace was given unto, moral perfection is attainable by fully submitting to and accepting this Grace.