Massey was a believer in spiritual evolution; he opined that Darwin's theory of evolution was incomplete without spiritualism:The theory contains only one half the explanations of man's origins and needs spiritualism to carry it through and complete it. For while this ascent on the physical side has been progressing through myriads of ages, the Divine descent has also been going on - man being spiritually an incarnation from the Divine as well as a human development from the animal creation. The cause of the development is spiritual. Mr. Darwin's theory does not in the least militate against ours - we think it necessitates it; he simply does not deal with our side of the subject. He cannot go lower than the dust of the earth for the matter of life; and for us, the main interest of our origin must lie in the spiritual domain.In regard to Ancient Egypt, Massey first published The Book of the Beginnings, followed by The Natural Genesis. His most prolific work is Ancient Egypt: The Light of the World, published shortly before his death. Published in 1907.Like Godfrey Higgins a half-century earlier, Massey believed that Western religions had Egyptian roots. Massey wrote,The human mind has long suffered an eclipse and been darkened and dwarfed in the shadow of ideas the real meaning of which has been lost to moderns. Myths and allegories whose significance was once unfolded in the Mysteries have been adopted in ignorance and reissued as real truths directly and divinely vouchsafed to humanity for the first and only time! The early religions had their myths interpreted. We have ours misinterpreted. And a great deal of what has been imposed on us as God's own true and sole revelation to us is a mass of inverted myths.One of the more important aspects of Massey's writings were his assertions that there were parallels between Jesus and the Egyptian god Horus, primarily contained in the book The Natural Genesis first published in 1883. Massey, for example, argued in the book his belief that: both Horus and Jesus were born of virgins on 25 December, raised men from the dead (Massey speculates that the biblical Lazarus, raised from the dead by Jesus, has a parallel in El-Asar-Us, a title of Osiris), died by crucifixion and were resurrected three days later. These assertions have influenced various later writers such as Alvin Boyd Kuhn, Tom Harpur, Yosef Ben-Jochannan, and Dorothy M. Murdock.