Explain the significance of the reenactment of the crime in The Moonstone?

In the book The Moonstone by Wilkie Collins, Franklin took the diamond under the influence of the drug, reacting to his anxiety about the safety of the gem. This hypothesis is proven when Jennings stages a reenactment of the night the gem was stolen, and Franklin replicates his actions exactly, again under the influence of opium. Franklin is vindicated, and Franklin and Rachel are reconciled and engaged. The reenactment was what proved the hypothesis of the crime.