Why is the following quote significant in The Scarlet Letter?

"Wherefore not; since all the powers of nature call so earnestly for the confession of sin, that these black weeds have sprung up out of a buried heart, to make manifest an unspoken crime?"

These lines also foreshadow the manifestation of Dimmesdale's sin that is upon his chest in Chapter XXIII, "The Revelation." At this time, too, Chillingworth is present; however, again Dimmesdale does not surrender to the physician: 

Old Roger Chillingworth knelt down beside him, with a blank, dull countenance [like black weeds], out of which the life seemed to have departed. "Thou hast escaped me! He repeated more than once."Thou hast escaped me!"

While Chillingworth has desired Dimmesdale's confession, it was only to him so that he could "own" the sin of the minister and thus control him.  However, Dimmesdale escapes through his public confession; he exposes "the black weeds that have sprung up our of a buried heart."

Chillingworth has gathered herbs from a graveyard and has returned with them to his room.As he prepares the herbs, he is talking to Dimmesdale, who is hiding his sin of adultery with Hester. Chillingworth comments that the "black weeds" which have sprung up from the graves are the result of unconfessed sin on the part of those who are buried there. This is an obvious reference to Dimmesdale's unconfessed "crime." and suggests that Chillingworth knows Dimmesdale's secret. However, Dimmesdale is not about to reveal himself to the old doctor and replies that many people live with secrets that they cannot reveal. Ironically, their conversation is interrupted by the the laughter of Pearl, who is playing below a window of the room in which the conversation takes place.