How do I get my 87 year father to bathe?

If you use the search bar on the upper right, and search for Bathe and refuse or won't, you will find LOTS of discussions, including advice on how to give a bed bath.

He may well be afraid of falling, and that is a real danger.

my mother only rag bathed for her entire life. these people grew up in a time where bathtubs and showers were rare or unheard of.

Call his MD and have OT (occupational therapist) come to the house and teach him how to safely get in and out of the tub. You may have to add some grab bars in the tub area.