Sins and faulty character seal off one's heart from holiness to the extent that it is impossible to see clearly as long as the soul is sullied by his sins and faults. To truly understand Divine truths one must first do teshuva.
For sins between man and G-d, teshuva immediately restores the light of the Divine spirit. But for sins between man and man, sometimes there are various factors which prevent us from rectifying them. The correct path is to take upon oneself not to repeat these sins again and Hashem will help him rectify these sins and the light of knowledge will be resored.
The Rav writes:
