The History of Rasselas, Prince of Abyssinia by Samuel Johnson

"What reason," said the Prince, "can be given why the Egyptians should thus expensively preserve those carcases which some nations consume with fire, others lay to mingle with the earth, and all agree to remove from their sight as soon as decent rites can be performed?"

"The original of ancient customs," said Imlac, "is commonly unknown, for the practice often continues when the cause has ceased; and concerning superstitious ceremonies it is vain to conjecture; for what reason did not dictate, reason cannot explain. I have long believed that the practice of embalming arose only from tenderness to the remains of relations or friends; and to this opinion I am more inclined because it seems impossible that this care should have been general; had all the dead been embalmed, their repositories must in time have been more spacious than the dwellings of the living. I suppose only the rich or honourable were secured from corruption, and the rest left to the course of nature.