Paul never denied that he was fleshly, a human being who had sin within him, and still Paul accepted that through Christ he took on being without sin: wiped clean of all his sin. He didn't let his humanness stop him from accepting the complete forgiveness offered him, or let it stop him from doing his best to be true to his sinless being.
Paul tells us in Romans 7:15 I do not understand what I do. For what I want to do I do not do, but what I hate I do. 16 And if I do what I do not want to do, I agree that the law is good. 17 As it is, it is no longer I myself who do it, but it is sin living in me. 18 For I know that good itself does not dwell in me, that is, in my sinful nature.[
a] For I have the desire to do what is good, but I cannot carry it out. 19 For I do not do the good I want to do, but the evil I do not want to do—this I keep on doing. 20 Now if I do what I do not want to do,
it is no longer I who do it, but
it is sin living in me that does it.