Both Brown and Gardner attest to the history of divine appellation to human government. In Egypt, the pharoah was considered the direct descendant of Isis and Osiris. It became customary for pharoahs to marry near-relations, even sisters, to keep the divinity within themselves pure.
The custom was known throughout the world, as Sir Laurence writes: "In fact, the concept dated back as far as the ancient kings of Mesopotamia, who were said to be born of Tiamat, the great mother of the primordial salt waters" (p. 150). Gardner had just stated that the Merovingians themselves, in their pre-Christian times, associated their lineage with "the Bistea Neptunis," and a god of old Arcadia named Pallas. Gardner summarizes by stating: "The immortal sea beast was said to be ever incarnate in a dynasty of ancient kings, whose symbol was a fish. This became an emblem of the Merovingian kings..."
Sir Laurence believes that this builds the case for the esoteric Grail quest. It does nothing of the kind. All it proves is that heathen nations ascribed divine origins to their kings, and by virtue of divinity, kings bore an absolute right to rule. To the extent that is true of the Merovingians it is not my expertise to say: For the sake of argument, I will grant that what Sir Laurence asserts here is the true practice of the Merovingians.
It would not be shocking, therefore, that new converts to the faith of Christ would syncretize their old practices. If Neptune or Poseidon are false gods but Christ is true, then it must be that I, the true king, am descended from Christ.
More far-fetched heresies have been hatched. Even in America's Bible-belt where scriptural literalism reigns supreme among the religious, hacks and self-proclaimed messiahs have risen up to claim divine power and messiahship. It is no great surprise, therefore, that Biblically illiterate cultures in which it was customary to ascribe divinity to royalty before the integration of Christian teaching, would continue to do so even after the establishment of the Church.
This becomes particularly important when rivals vie for the throne, each with claims they esteem to be legitimate. Who better to bear rule than the true Son of David, goes the logic, since we are Christendom. Yet the scriptures allow for no such interpretation, so these heresies become the meat of secret societies of knights bound by oath to this or that claimant.
All of this presumes that the Merovingians themselves made such claims. Whether they made any such claim at all is a matter of history about which, were we to grant it to the esoteric Grail Quest, would be to lower the bar of skepticism enough to allow for at least that much speculation and conversation. But if we do grant the esoteric Grail Quest this much, that the Merovingians made such claims, we already see the origin in heathen custom syncretized with the new "gods" of Christian faith.
What we know as a fact is that His Royal Highness Prince Michael of Albany in Scotland makes such a claim for himself as the author of the forward to Sir Laurence's book. He is the heir to the House of Stewart, a claimant doomed to be runner-up after the deposing of James VII in favor of William of Orange three hundred twenty years ago. Centuries later the claim of divine lineage is set forward by his official historian, Sir Laurence Gardner, a claim that HRH Prince Michael would be foolish not to embrace. At stake, after all, is a royal fortune worth billions, a place in history, and the vindication of the Stewarts after centuries of ignonimy.
Think of the appeal of this notion to white people, especially people of Scotch-Anglo origin such as myself. (Indeed, to get an idea of what I look like, download a picture of HRH Prince Michael and then shade in a short-cropped red-brown beard.) A true Scottish prince is actually the Lion of Judah, the Son of David, given divine right by God to rule as God's own anointed, the Christ on Earth! That would make me, what, one of the Chosen People?
Will all esotericists agree with Sir Laurence? Perhaps not. However, esotericists such as Dan Brown could not shake the unconscious assumption that somehow the Christ must be White. Remember, we discover Sofie's long-lost brother, the male descendant of Jesus and Mary Magdalene, is living where? In Scotland. He is even red-headed, for good measure!
Heathen superstitions die hard. Jesus of Nazareth became a substitute divinity for Neptune or Poseidon or Pallas, pagan gods who conceived human children. As Christian faith, teaching, and literacy advanced, superstition receded into secrecy. Still, the claim of divinity surfaces when it can come in handy - the machinations of HRH Prince Michael is proof that politics knows no tool it cannot use.
It is interesting that the claim is made by the pretender to the throne, while the Windsors (formerly Hanovers) make no such divine claim for themselves. They do not need to - their succession is legitimized by law.