As pretty much everyone has said, the Bible was a prop. I don’t know any religious leader that has approved of it, so why do it? If all he wanted to do was show off somebody’s Bible, he didn’t have to flash bang protesters and gas them for his photo op outside a church across from the White House.
I can only make an informed guess why he did this, but I think Trump was harkening back to Hitler, either intentionally or accidentally, and the message is: “The strong rule by divine right.”
An associate of Hitler, Albert Speer, wrote:
I can only explain Hitler’s rigid attitude on the grounds that he made himself believe in his ultimate victory. In a sense he was worshiping himself. He was forever holding up to himself a mirror in which he saw not only himself but the confirmation of his mission by divine Providence. His religion was based on the “lucky break” which must necessarily come his way; he method was to reinforce himself by autosuggestion. The more events drove him into a corner, the more obstinately he opposed to them his certainty about the intentions of Fate. Naturally, he also soberly understood the military facts. But he transmuted them by his own faith and regarded even defeat as a secret guarantee, offered by Providence, of the coming victory. Sometimes he could realize the hopelessness of a situation, but he could not be shaken in his expectation that at the last moment Fate would suddenly turn the tide in his favor. If there was any fundamental insanity in Hitler, it was this unshakable belief in his lucky star. He was by nature a religious man, but his capacity for belief had been perverted into belief in himselfAlbert Speer, Inside the Third Reich : memoirs
And Hitler himself wrote:
Nature…puts living creatures on this globe and watches the free play of forces. She then confers the master’s right on her favorite child, the strongest in courage and industry…The stronger must dominate and not blend with the weaker, thus sacrificing his own greatness. Only the born weakling can view this as cruel.Mein Kampf
This photo-op occurred after Trump told state governors that they must dominate, or look like jerks. What Donald Trump did was obscene and against the laws of God and man.