Ooo, I posted the below but while I was writing it Vox posted the above. So it seems that the below is correct but only after level 6 when the Sacred Fist is automatically granted the Divine Dream feat.

*Thanks Vox!
Hello. I went to ddowiki.com and looked at the Sacred Defender Enhancement tree. Many of the enhancements in the tree are tied to the Sacred Defense stance which is usually predicated upon wearing medium armor, heavy armor, or a shield.
However, in the text box for Sacred Defense (2nd Core enhancement) is this text: "
Note: The enhancements which require wearing Medium/Heavy Armor or Shields, also work for
Sacred Fist as long as they are
centered (uncentering removes these bonuses)."
Sooo...for Sacred Fist being centered fulfills the prerequisites that are normally filled by the armors or shield.
Here a link to that page:
https://ddowiki.com/page/Sacred_Defender_enhancements