A person should never say “I am so unclean because of my transgressions and impure thoughts, how can I study Torah and defile its glorious beauty? I will wait until I purify myself and then I will study Torah with pure motivations.”

This is not proper.  A person needs to study Torah in order to overcome his evil inclination.  By studying Torah in a state you are in, you will elevate yourself. ~ R’ Chaim of Volozhin zt”l