I saw believers damn their Past Sinful Life. They keep those things in their mind and that is why they fail to overcome it. And Satan wisely uses the same to slow down their Christian race.

     On the same topic Paul said "I am Chief Sinner" (1 Timothy 1:15) but only to testify the love and grace of our Lord Jesus Christ. Because He is fully confident that though He was Chief Sinner yet He is forgiven. And Christ made all things new (2 Corinthians 2:17) in his life and made Him Ideal/Model for many who believe (1 Timothy 1:16). 

     My friend - You have the same case. So don't damn your past because old things (old thoughts, old principles, old practices) are passed away and all these things have become new.