Our sins have been washed away by The Blood of Jesus Christ with His sacrifice on The Cross at Calvary. However, our sin conscience is ever present with us in our flesh. Being it most difficult to control the thoughts that are in our mind because of our fleshly sin-nature, we should learn that as we pray to always repent for our sins of not only our words and actions, but sinful thoughts that may manifest themselves in our minds on a daily bases.
"Lord, have mercy upon me, a sinner. . . I repent for all of my sins both knowingly and unknowingly, and those committed in the thoughts of my flesh."