What did Jefferson intend to say by Plato's "whimsies into the body of artificial Christianity"?

Question

Source: The Well-Educated Mind (2 edn 2016), p. 49 Middle.

  If you don't have a reading partner who can meet with you face to face, you can conduct discussions by letter (or email, as long as you treat these dialogues as formal, requiring proper vocabulary, grammar, spelling, and punctuation, not resorting to the shorthand of e-communication). In 1814, Thomas Jefferson, obviously feeling isolated on his Virginia mountaintop, wrote to John Adams that Plato is

one of the race of genuine sophists, who has escaped the oblivion of his brethren, first, by the elegance of his diction, but chiefly, by the adoption and incorporation of his whimsies into the body of artificial Christianity. His foggy mind is forever presenting the semblances of objects which, half seen through a mist, can be defined neither in form nor dimensions.... But why am I dosing you with these antediluvian topics? Because I am glad to have some one to whom they are familiar, and who will not receive them as if dropped from the moon.²

Answer 1

By "Plato's whimsies" he almost certainly means the idea of the Ideal Forms, or more in general, the metaphysical idea of their being another layer of "Reality" deeper and more real than our own, and from which our own is a forever imperfect copy. These ideas were made explicitly religious by the Neoplatonists, and then incorporated into Christian theology via the work of St Augustine and other early Christian theologians --this work being the "artificial Christianity" Jefferson is also deriding.

Jefferson describes Plato's Ideals as foggy and misty. This is because of Plato's claim that we can only grasp them in part here (in the ordinary world), and that any version of them we envision is necessarily incomplete and inaccurate. Jefferson's language probably deliberately echoes St. Paul's famous metaphor of "seeing in a mirror, darkly" as the natural condition of moral, earthly life. Also note that his description of Plato as a "genuine sophist," is a backhanded compliment at best, since Plato consistently portrayed the sophists (who were pre-Socratic philosophers) as superficial wisdom peddlers constantly being bested by Socrates. (This would be like calling Jesus a "genuine Pharisee.")

Jefferson is further suggesting that it is only because of (what he would probably view as) the historical accident of a syncretic synthesis of Christian and Platonic ideas that Plato's reputation and philosophies survive at all, despite what he sees as their blatant silliness. His last statement implies that most modern thinkers wouldn't give such obsolete ideas even the ghost of a thought, but that it is enjoyable to talk them over, even dismissively, with someone else educated in the ancient Classics and Christian theology. (It is, however, worth noting that we still study Plato, even two more centuries past the time of Jefferson. Furthermore his "whimsies" were already 300 years old at the time of Christ --and twice that by the time Augustine learned them.)