Era of tolerance, religious cross-pollination.
There was an era in Norway between the era of the old Celtic missionaries living in with the homesteads and their chapels, and dealing mildly with the local kings, to the institutional takeovers where dogma was compelled. In that era, old beliefs were tolerated, many were similar anyway, or shared symbols and ideas, and even stories of gods and god-figures. In those eras, ideas were allowed to blend and enrich, the newcomer Christian story of origins and the meaning of life. The earliest stave churches reflect that. They even look oriental.
Start your own research. Look up The Dragon, the Snake, the Serpent. Commonalities with Christian stories as well. These were not alien ideas.
The dragon with its extended neck, and serpents twining, striking, hold a prominent place in the world's mythologies, see Dragon at http://www.bartleby.com/81/5323.html/ Dragons and sea serpents and the Midgard Serpent Jormungandr of Norse mytho, encircling the earth. As Apollo overcame a dragon at the place we know in Greece as Delphi, so in one view of religious life, the dragon represents an evil that must be overcome. See http://faculty.arch.utah.edu/miller/Stave%20Churches_001.pdf. To old Norse, the dragon stemmed from the world's beginnings, was close to the view of the sea serpent, http://www.princeton.edu/~achaney/tmve/wiki100k/docs/J%C3%B6rmungandr.html
See the overview of what is left of the old stave churches at http://www.arild-hauge.com/echurch.htm
- Everywhere the dragons could be lopped off and a cross easily substituted, do it: The jvariety in rooflines remained for many, with the multiple tiers, the outside galleries, the many ways in and out, the dimness of the interior, standing only, remain. In others, where the original had been destroyed, as by fire, or rot, economies took over. That is one explanation for the austerity, the prim stance of too many "restored" stave churches.