Final answer:
The author is comparing the action of digging into the clergyman's heart to a sexton delving into a grave. This comparison suggests that the act of delving into the clergyman's heart is like uncovering something hidden or buried.
Step-by-step explanation:
The author is comparing the action of digging into the clergyman's heart to a sexton delving into a grave. This comparison suggests that the act of delving into the clergyman's heart is like uncovering something hidden or buried, possibly in search of a valuable jewel. However, the author also suggests that what is likely to be found is mortality and corruption, emphasizing the negative and dark aspects of the clergyman's heart.