Answer:
It means that the walk from the prison-door to the marketplace seems trecherous and long to Hester Prynne.
Explanation:
Nathanael Hawthorne's "The Scarlet Letter" is about the story of Hester Prynne, a woman convicted of adultery, and the "punishment" that was given to her. The novel also deals with themes of society, religion, good vs. evil, public shaming, social stigma, etc.
In the given excerpt, the narrator is talking about the "walk" from the prison door to the marketplace where Hester will be 'on display' for the public to see. The narrator reveals, "measured by the prisoner's experience, [the walk] might be reckoned a journey of some length" which is how it was more of "an agony from every footstep" for Hester. These lines show how Hester thinks the walk is long and treacherous for her.
