Why does Mal'akh give Langdon a second chance in the novel, The Lost Symbol?

Mal'akh respects Langdon's dedication to seeking the truth, so he not only shows Langdon the place where the Ancient Mysteries are buried, he also rewards rewards him with the opportunity to see the sun rise over the Washington Monument from the dome of the Capitol Building. This experience reignites Langdon’s hope that the light will over come the forces of evil in the world.