In particular, three parallels are set up to striking effect in the novel.
First, Silas is explicitly paralleled with Bartley Hubbard, the cynical journalist who interviews him in the novel's opening chapter. This is likely done to reflect how hungry young people are for success at any cost, as well as to show the irony of Bartley's cynicism. After all, he may wind up striving too hard and failing, just like Silas.
Second, Silas is also paralleled with Tom Corey because they share a strong work ethic. This explains one reason that Irene (who is more similar to Silas) fails in courting Tom where Penelope succeeds (since she is more like Persis, and more clever than Irene and Silas). Additionally, this parallel provides a pathway for explaining how Boston society might advance past its old money roots—with the effort of hard workers, like Silas (new money) and Tom (new thinking).
Finally, the correspondence between Penelope's personal anguish over the Tom-Irene situation is meant to parallel the conflict presented in the Romantic novel "Tears, Idle Tears." This not only shows the absurdity of Penelope's choices with regard to her love triangle, but also demonstrates that when personal conflicts arise, it can be hard to think rationally and act properly.