"mortal or venial or only imperfections" 

From The Catholic Encyclopedia: 

"Mortal sin is defined by St. Augustine (Contra Faustum, XXII, xxvii) as "Dictum vel factum vel concupitum contra legem æternam", i.e. as something said, done or desired contrary to the eternal law, or a  thought, word, or deed contrary to the eternal law.

• "The first effect of mortal sin in man is to avert him from his true last end, and deprive his soul of sanctifying grace.
   
• "The second effect of sin is to entail the penalty of undergoing suffering (reatus pænæ). Sin (reatus culpæ) is the cause of this obligation (reatus pænæ ). The suffering may be inflicted in this life through the medium of medicinal punishments, calamities, sickness, temporal evils, which tend to withdraw from sin; or it may be inflicted in the life to come by the justice of God as vindictive punishment.

"Venial sin as it is a voluntary act may be defined as a thought, word or deed at variance with the law of God. It retards man in the attainment of his last end while not averting him from it.

• "Venial sin does not deprive the soul of sanctifying grace, or diminish it. It does not produce a macula, or stain, as does mortal sin, but it lessens the lustre of virtue."

Hence, mortal sin stains and threatens the very soul; venial sins do not. Imperfections are simply the lot of imperfect humankind, less serious than venial sins, for they do not involve volition.