After watching innumerable corpses being taken to the burying pit in the City of London, the narrator cannot control his curiosity and goes to the pit in order to see how the massive number of bodies are buried.  The Sexton takes great pains to dissuade the narrator from going into the burying pit--arguing, for example, that the clergy may have to risk their lives but the narrator does not--but the narrator's response is

I told him him I had been press'd in my Mind to go, and that perhaps it might no be without its Uses.

In other words, the narrator appeals to the Sexton's belief that the sight of these burials may bring the narrator closer to his own salvation.  The narrator's curiosity may be the cause of his going into the burying ground, but the result may actually be some spiritual enlightenment that the narrator would otherwise not experience.  Although the warning causes the narrator to pause for a few moments, as soon as he hears the next "Dead-Cart" approaching, he decides to go in.

The Sexton's belief in the instructional possibilities of the experience is so strong  that he essentially agrees with the narrator:

Nay, says the good Man . . . if you will venture upon that Score . . . 'twill be a Sermon to you, it may be, the best that ever you heard in your Life.  'Tis a speaking Sight, says he, and has a Voice with it, and a loud one. . . .

Espousing the belief in the value of first-hand experience, the Sexton cannot refuse the narrator an experience that might bring him closer to repentance and ultimate salvation.