Whenever one encounters a proposed example of pagan influence, one should demand that its existence be properly documented, not just asserted. The danger of accepting an inaccurate claim is too great. The amount of misinformation in this area is great enough that it is advisable never to accept a reported parallel as true unless it can be demonstrated from primary source documents or through reliable, scholarly secondary sources.
After receiving documentation supporting the claim of a pagan parallel, one should ask a number of questions:
1. Is there a parallel?
Frequently, there is not.
The claim of a parallel may be erroneous, especially when the documentation provided is based on an old or undisclosed source.
For example: "The Egyptians had a trinity. They worshiped Osiris, Isis, and Horus, thousands of years before the Father, Son, and Holy Ghost were known" (Robert Ingersoll, Why I Am an Agnostic).
This is not true. The Egyptians had an Ennead—a pantheon of nine major gods and goddesses. Osiris, Isis, and Horus were simply three divinities in the pantheon who were closely related by marriage and blood (not surprising, since the Ennead itself was an extended family) and who figured in the same myth cycle.
They did not represent the three persons of a single divine being (the Christian understanding of the Trinity). The claim of an Egyptian trinity is simply wrong. There is no parallel.
2. Is the parallel dependent or independent?
Even if there is a pagan parallel,
that does not mean that there is a causal relationship involved. Two groups may develop similar beliefs, practices, and artifacts totally independently of each other.
The idea that similar forms are always the result of diffusion from a common source has long been rejected by archaeology and anthropology, and for very good reason: humans are similar to each other and live in similar (i.e., terrestrial) environments, leading them to have similar cultural artifacts and views.
For example, Fundamentalists have made much of the fact that Catholic art includes Madonna and Child images and that non-Christian art, all over the world, also frequently includes mother and child images. There is nothing sinister in this.
The fact is that, in every culture, there are mothers who hold their children!
Sometimes this gets represented in art, including religious art, and it especially is used when a work of art is being done to show the motherhood of an individual. Mother-with child-images do not need to be explained by a theory of diffusion from a common, pagan religious source (such as Hislop’s suggestion that such images stem from representations of Semiramis holding Tammuz).
One need look no further than the fact that mothers holding children is a universal feature of human experience and a convenient way for artists to represent motherhood.
3. Is the parallel antecedent or consequent?
Even if there is a pagan parallel that is causally related to a non-pagan counterpart, this does not establish which gave rise to the other.
It may be that the pagan parallel is a late borrowing from a non-pagan source.
Frequently, the pagan sources we have are so late that they have been shaped
in reaction to Jewish and Christian ideas. Sometimes it is possible to tell that pagans have been borrowing from non-pagans. Other times, it cannot be discerned who is borrowing from whom (or, indeed, if anyone is borrowing from anyone).
For example: the ideas expressed in the Norse Elder Edda about the end and regeneration of the world
were probably influenced by the teachings of Christians with whom the Norse had been in contact for centuries (H. A. Guerber, The Norsemen, 339f).
4. Is the parallel treated positively, neutrally, or negatively?
Even if there is a pagan parallel to a non-pagan counterpart, that does not mean that the item or concept was enthusiastically or uncritically accepted by non-pagans.
One must ask how they regarded it. Did they regard it as something positive, neutral, or negative?
For example: circumcision and the symbol of the cross might be termed "neutral" Jewish and Christian counterparts to pagan parallels. It is quite likely that the early Hebrews first encountered the idea of circumcision among neighboring non-Jewish peoples, but that does not mean they regarded it as a
religiously good thing for non-Jews to do.
Circumcision was regarded as a religiously good thing only for Jews because for them it symbolized a special covenant with the one true God (Gen. 17). The Hebrew scriptures are silent in a religious appraisal of non-Jewish circumcision; they seemed indifferent to the fact that some pagans circumcised.
Source.