When you look at Romans 1 and 2 it builds up to 2:28 and 29. Having talked through man's attempts to be satisfied with his own righteousness, be that the law, circumcision, worshipping creation rather than the Creator etc. Paul now faces us with the reality that God needs to do a work on our hearts. As christians He will continue to do that throughout our lives. We need therefore to allow him to remove any hardness in our hearts and help us to remain open to His work.