Or HaChaim on Genesis 50:2/אור החיים על בראשית נ׳:ב׳

1 ויחנטו הרופאים את ישראל. The physicians embalmed Israel. Joseph initiated this procedure because of the honour due to his father. All men of stature were embalmed, especially those connected with royalty. Alternatively, Joseph arranged for the embalming in order that people should not say that Jacob had not died or that he had died but that his body did not putrify and they would idolise him as a result. Besides, if that were to happen he would never secure permission to bury his father in the land of Canaan. Had Joseph not ordered embalming, Jacob's "body" would not have putrified. It is interesting to read the story in Baba Metzia 84 concerning the body of Rabbi Eleazar son of Rabbi Shimon bar Yochai which had lain in an attic for years without signs of decay.

2It is also possible that ever since the Israelites who stood at Mount Sinai rid themselves of the residual pollution by the original serpent, the bodies of the righteous of our nation no longer putrified after their deaths (Shabbat 146). Accordingly, even the mould within their entrails simply dried out and turned to dust without leaving behind any offensive odour seeing it is only the pollution associated with the original serpent which causes the food within the entrails to become putrid. Although it is said of Jacob that he did not die, the mould inside his entrails which remained within his body was apt to turn putrid. Joseph was concerned about that aspect and that is why he had his father's body embalmed.

3It is also possible that Joseph was unaware of these secrets when he ordered his father to be embalmed.