Why did Ba and Ka from ancient Egypt need to know if a dead body was decayed?

Answer 1

Your Akh is that which resides amongst the stars.......

Your Ka is your life force and your spirit... a guardian spirit that rejoins with your Ba upon your death.

Your Ba is the soul of the body itself...separate during life from teh Ka and Akh... but joined with the Ka afrer death.

Your Ka and Ba ascend at some point after judgement to the waiting Akh in the stars above.

You forgot two very important parts of your Egyptian Human Personality; Your Name and your Shadow.

You cannot ascend without both intact and your Name prominently remembered by your loved ones enough so that you can ascend properly.

The Shadow melds with your Ka and Ba upon your death as well, but watches over your body and your name....

Answer 2

The various aspects of the soul needed a home, for lack of a better term, and that home was the physical body. Identity was linked to a person's name and their physical body. In order for the soul (and its various component parts) to survive an image of the person needed to survive. Ideally, this was the body of the person. However, statues of the person or even, in some cases, just the inscription of a person's name was sufficient to ensure their immortality.