The Origin of Origins

I've come across the old saw about Christian holidays being little more than "borrowings" from old pagan festivals, and although there is truth there, the facts are far hazier (like a lot of history) than people are willing to acknowledge.

Really, the question comes down to this: which came first? True worship of God or pagan festivals? Did pagans invent rest and festival or did God first rest on the sabbath?

Is Christianity truly a latecomer, so informed by the pagan world that surrounded its own nativity that it becomes impossible to separate it from "worldliness" except by strict surgical methods? (i.e. Eschewing Christmas, Easter, All Hallow's and adhering to a stern "1st century Christian" practice) Does sola scriptura extend to all practices, not just theology? If so, how does one recognize St. Paul's appeal to personal conscience (which is scriptural, obviously)?

What, then, do we do about Melchizidek? How do we explain the seed of Christian belief that is planted at cursing of Satan in the Garden?

In Genesis, we see the birth of pagan festival ("you will be like gods") almost concurrent with the seed of Christian faith ("He shall crush your head.") The author of Hebrews reflects on Genesis when he speaks of the faith of Abel, of Enoch, of Noah, etc. all of whom "were sure of what they hoped for, and certain of what they did not see."

What was it that these early people hoped for? What was it that they did not see?

Christ.

The primacy of Christ is well acknowledged, but somehow, we resort to fallible human histories when worrying about the "pagan origins" of Christian practice. What then, are the true origins of pagan copies? From what do they draw their inspiration?