In A Tale of Two Cities, how does the title "Substance of the Shadow" Book 3 Chapter 10, relate to the chapter?

In this chapter, Doctor Manette reads the confession and curse that he wrote many years before when he was imprisoned in the Bastille. This is the secret (the shadow) that he has carried all this time, which relates to the secret of Charles Darnay’s connection to the Marquis of Evremonde and to the Doctor. He reveals that he had helped the victim of Charles’s father’s violence, who also happened to be Madame DeFarge’s sister-in-law and family. It is for this reason that Madame de Farge denounced Charles to the tribunal, leading to his arrest. The Doctor, in his despair, cursed the Evremonde family forever, and in this way also served as a denouncer of Charles, despite the fact that he had no idea that Charles was an Evremonde until the morning of Charles’s wedding to his daughter Lucie. This revelation thus gave substance to the shadow of these secrets.