To figure this out, you would need to look up what eggs symbolize in whatever culture/religion/practice your grandfather was involved with. Symbolism depends quite a lot on location and religion. Most agree that it is a symbol of birth, creation, and motherhood. The yolk of the egg resembles the sun, and can also be used to represent it. As ladygrey stated, eggs, along with onions and potatoes are most commonly used as "absorbing" items that are used to pull illness or negativity from a body or room, and then discarded or destroyed afterward.
From what I know from experience and literature, this article is very accurate.
Eggs can also be used to break fevers by placing the whites on the bottom of the sick person's feet (I drop the egg whites in a pair of socks, put it on their feet, wrap it in plastic wrap, then put clean cotton socks over the plastic). I've done this for my daughter before, and it broke her 102F fever in 30min flat. (Be sure to wash your own hands and their feet well afterwards because eggs can carry bacteria). I'm explaining this because (1) I can foresee pms asking me how to use eggs for fevers if I didn't explain thoroughly lol and (2) I wanted to give an example of how eggs can be used in medicine. What your grandfather performed could have been some form of healing. I chant over anything I use to heal myself or my family, even chicken soup.
3 is symbolic as well. For me it is mind, body and spirit.