Something prohibited even by Rabbinic enactment remains attached to the three unclean kelipot and cannot be elevated to holiness, even when it is used unwittingly and for the sake of heaven (i.e., in order to have the strength to study and pray). Once the person has committed the act, a residue of the evil will attach to him, even once repentance has been completed. A cleansing of the soul will be necessary at the end of one's life to remove this.