Pretty clear that Biden thinks fighting to a bitter end is better for his Legacy than resigning.
What it means for his party is not so clear.
It is also not a vote of confidence for Kamala
I think Biden feels.he can still do the job and is the Dem's best chance to eat Trump. Whether he is right on either of those two things is very much open to question. Things like his debate performance feed into an existing narrative and are really, really hard to undo.
I think that it says nothing about his faith in Harris, but everything about his combativeness. He would do the same regardless of his Veep.
Note: I appear to have hit the space bar instead of a B, but I am keeping it in.