Although some art historians support the authors' observations, they draw different conclusions. Lev insists that one can't "separate the painting of the chapel and this great vision of man, from the context in which it was painted, which is of course a Christian context -- the pope, this court, the New Testament and Christ."
Blech points out that none of the figures on the ceiling are Christian, suggesting that Michelangelo was straying from traditional Catholic iconography.
"By emphasizing only Old Testament figures in the entire ceiling … what he was trying to say was why we have ignored our true roots."
But not all of the figures are from the Old Testament. Next to the Jewish prophets, Michelangelo painted five pagan sibyls from ancient Greek mythology. Scholars in Renaissance Italy were looking outside the Christian world to bolster their theology. Even in the papal court, theologians were exploring other philosophical and religious traditions.
Despite the unorthodox influences, which he acknowledges could be reflected in the panels' details, Wallace says Michelangelo was a devout Christian.
"Michelangelo does nothing but become more and more profoundly Christian all through his life," Wallace said. "However, this is the moment of exposure to the world of pagan antiquity … which is not in any way contradictory, but complimentary to a Christian theology."
Arnold Nesselrath, curator of the Vatican Museums, dismisses the Kabbalah references.
"Well, we have all to remember that this is the palace chapel, the main chapel of the Vatican palace, and whatever Michelangelo is painting here had to be discussed with the pope and his advisers."
The authors of "The Sistine Secrets" claim that Michelangelo was furious at Pope Julius II, who commissioned the work. Michelangelo was a sculptor, not a painter, and was angry to put his sculpture career on hold to paint frescoes. They say that anger caused the artist to paint hidden references to the corruption of the papacy of his time.
"All these things upset Michelangelo very much. My own personal feeling is that Michelangelo had to get this off his chest," Blech said.
Monsignor Timothy Verdon, art historian at Stanford University, Florence, said, "It's a bit hard to think that Michelangelo could have been deeply concerned with great questions of church reform."
However, scholars agree that the patron and artist had a rocky relationship.
Michelangelo's earliest biographers reported that he threw planks down from the scaffold when the pope tried to sneak a peek at the unfinished ceiling. They also wrote that Julius beat Michelangelo in public. But Wallace believes he would have gotten over it.
"[Michelangelo's] enormously ambitious," Wallace said. "The pope is giving him an opportunity to create one of the greatest works of art of all time."
He concedes that Michelangelo was resistant and even resentful at the start of the project, but does not believe these feelings continued after he began to paint. His patron was the head of the church and "that's plenty to keep you working."