In addition to those scratches there's also a dent that needs to be hammered out.

The scratches need to be sanded out. I'd start with a DA and 220 grit until you cant see the scratches anymore. The sanding will also reveal any low spots (like that dent). After the dent and scratches are gone I'd move up to 400, 600, then 800 grit with the final sanding done in the direction of the grain.

It'll look new when you're done.

Here's an old Williams door I did as described above that was in way worse shape than yours. (Actually I think I stopped at 600 grit on this one... I don't remember)
RB89 (resized).jpg
RB90 (resized).jpg

Hope this helps

-Paul

This is very true.

The purpose of going to finer and finer grits is to remove the scratches from the previous sanding. In your pics you can still see those sanding marks from previous grits.

If you want to polish the door to a high shine you'd continue sanding to the much finer grits (1500, 2000... etc) before a final polish.

If you want to make it appear stock you'd want to finish with a 400 or 600 grit sanded in the direction of the grain. Yours is now kind of in between those two. I've also finished a door with red scotchbrite to make it appear stock.
IMG_20191208_211124678 (resized).jpg
(sorry I don't have a closeup pic of the door, but it's a stock satin-like finish)

Experiment with it a bit with different grits. It looks like you got the dent, and the scratches out so now you have a nice, clean straight door. Just use whatever grit you can to give you the desired finish you like.

-Paul