Apply some penetrating finish to the scratch. Make sure to choose a finish that matches the stain already on the door. An oil-based stain that is slightly lighter than the original stain will help the scratch blend in without darkening the wood too much in areas that end up with more than one coat of stain.
Rub the finish onto the scratched area with a fine steel wool. Alternatively, stain the scratch with iodine to help it blend in with the color of the rest of the wood.
Allow the stain to dry thoroughly, and avoid touching the repaired area until it dries.
Rub paste wax onto the door.
Buff the paste wax with a soft cloth. Continue buffing the wax until it fills in the scratches and hardens on the wood.
Buff the wax with an electric buffer if the scratched area is large. Buffing by hand works fine, but an electric buffer works well for people with arm and shoulder injuries or who do not have enough strength to vigorously buff the wood.
Melt the end of a wax stick or shellac stick.
Fill the scratch in with the melted wax or shellac stick. Liquid shellac will also work to fill the scratch in, but the door must first be taken off of its hinges and laid horizontally to prevent the shellac from running out of the scratch.
Heat up a metal spatula or putty knife and use it to help work the wax or shellac into the scratch and fill it completely.
Scrape off any excess wax or shellac with a razor blade.
If you used a shellac stick to fill in the scratch, sand the area with 400 grit sandpaper coated in paraffin oil.