If your heart could do this good thing of sincerity prior to its being regenerated, then your heart was not "deceitful above all things and desperately wicked..."
Why was your heart not deceitful above all things and others have hearts that were deceitful above all things?
And why does the Bible proclaim a sinful heart to be the birthright of all humanity, for it clearly says that "no good thing resides in me."
Except God says otherwise - explicitly.
"But to all who did receive him, who believed in his name, he gave the right to become children of God, who were born, not of blood nor of the will of the flesh nor of the will of man, but of God."
"these are written so that you may believe that Jesus is the Christ, the Son of God, and that by believing you may have life in his name."