If a person is "truly and deeply nothing" then how is that person making decisions? I can understand feeling like nothing - but something has to exist to have a feeling of nothingness in the first place.
This is not nihilism. As I said, understanding the astonishingly small (and basically non-existent) nature of your life is one of the necessary steps to understand what it really means to exist in the first place. That is, as Paul says, if you think you are X or Y, then you are never freed to be a better version of yourself. This is because you are comparing yourself to some external standard that you can never be. Likewise, if you think that somehow "being a better person" is a journey that leads you somewhere that has lasting consequences you are also lying to yourself -- it really doesn't matter. What you need to understand that it is the daily decisions to be a better person that matter, not the comparison between yourself today and some future state that you are headed towards. This is the same mistake that Paul describes, only he is talking about comparing yourself to some label, while I am talking about comparing yourself to some future version of yourself that you are headed towards.
Does that make sense?
I love the near-perfect unintentional parody of the Jewish tale of three old men arguing over who was most unworthy.