Before you were saved you most probably thought you were a good person, right? The truth is, that most of us do. Because we judge ourselves against one another, we see ourselves as "okay", or "not as bad as Joe Blogs". The thing is, God's standard of good is perfection and against this measurement we ALL fall short... that's why we accepted Jesus in the first place though, isn't it?
8 If we claim we have no sin, we are only fooling ourselves and not living in the truth. 9 But if we confess our sins to him, he is faithful and just to forgive us our sins and to cleanse us from all wickedness. 10 If we claim we have not sinned, we are calling God a liar and showing that his word has no place in our hearts. (1 John 1:8-10, NLT)
To receive salvation we have to get to a place where we accept the conviction of the Holy Ghost. His conviction reveals to us that we are guilty. It's only in acknowledgment of this truth that we can find salvation in Christ. It's only when we choose to accept that God is true and we ourselves have lived a lie that we can be cleansed from all our sin.
In refusing to acknowledge sin, a person cannot receive salvation and His cleansing power because they are in calling the only One able to help them a liar. Only when a person humbles themselves, can God's word dwell in their hearts, taking them from darkness to light.