In addition to providing more information, does chapter 21 serve any other purpose?

Chapter 21 provides a climactic tension that has been brewing for much of the novel The last time we recall the public square filled with people was at Hester's branding. Although the occasion is different this time, a new governor is to be installed; much of the same atmosphere exists. People are not willing to forget that Hester is branded even though she is about to become "free" again. Hester, in turn, still suffers from the same emotions that she had on the day of her lettering. So, things have come full circle. The context is, however, different. Dimmesdale seems happy about his plans for escape but inside he suffers from the same anxieties that he had before. So, Ch 21 brings all the bubbling tension to a boil in the same setting as the beginning of the book. What we know about these characters now adds so much to the equation. Chapter 21 perfectly sets the stage for the unforgettable climax.