This was true in the Greek, Persian, Egyptian, and Hindoo mythologies. Back of the many, and beyond the transient and contending divinities, was the One, postulated, but unknown and changeless.
Every religion known to man, with the advancing civilization of a people, copied, modified, adopted, and adapted the mythology and folklore of some pre-existing religion and people. This is readily demonstrable with the Hebrew, Greek, and later Christian dispensations, notwithstanding the most strenuous and persistent determination to deny, disprove, and destroy the ancient records.
It is embodied in the etymology of the very names of heroes, gods, and demigods. A new language arising with any people de novo can nowhere be found.
Phonetics and picturegraphs, the various alphabets and glyphs, are mixed and modified, but never invented nor altogether changed.
Complicated as they may be, it is thus that philology, ethnology, theology, and anthropology constitute a consistent whole, the mythology and folklore of mankind. This reveals the practical unity and solidarity of the human race.
The tradition and prophecy among the ancient Hebrews of the coming of the Messiah, the portents that heralded, and the signs and wonders that preceded or accompanied his appearance, are merely translations or adaptations from previous eras, Buddhas, or Avatars.
Whether Christian or non-Christian, the object of the advent is always identical.
The light of the spirit having become enfeebled or obscured, the people are left in darkness and given over to sin and wickedness. Moral ruin seems inevitable unless there is a divine influx, a new Avatar, or Buddha, or Advent of the God-man.
God incarnates himself as the son of Mary, and Jesus says, “I am come a light into the world that whosoever believeth in me should not abide in darkness.”
Christna says, “Though I am unborn, and my nature is eternal, and I am the Lord also of all creatures, yet taking control of my nature-form, I am born by my illusive power. For whenever piety decays, O son of Bharata, and impiety is in the ascendant, then I produce myself. For the protection of good men, for the destruction of evildoers, for the re-establishment of piety, I am born from age to age.” (Bhagavadgita.)