As the Reverend Dimmesdale mounts the scaffold in this third scene with the place of ignominy for the Puritans, he calls to Hester and Pearl, his family. Although his face is ghastly, there is something "strangely triumphant in it." Hester, impelled by "inevitable fate," draws near against her will, but pauses before she reaches Dimmesdale. Just then, the Satanic Roger Chillingworth appears like the devil "to snatch back his victim from what he sought to do." Catching the minister by the arm, he urges the minister to
"Wave back that woman! Cast off this child. All shall be well! Do not blacken your fame, and perish in dishonour! I can yet save you! Would you bring infamy on your sacred profession?"
"Ha, tempter! Methinks thou art too late!" answered the minister, encountering his eye, fearfully, but firmly. "Thy power is not what it was! With God's help, I shall escape thee now!"
Extending his hand to Hester, Dimmesdale tells her that the old man opposes him "with all his own might, and the fiend's...Support me up yonder scaffold." As the minister confesses his sin to the public, Chillingworth bemoans, "Thou has escaped me!" and Dimmesdale tells him,"May God forgive thee! ...thou, too, hast deeply sinned!"
This, of course, is the climax of Hawthorne's novel as the Reverend Dimmesdale reveals his secret sin and clears his tortured conscience. With the peace in which Dimmesdale perishes, the theme of Hawthorne is illustrated. It is the hypocrisy of the Puritan who feels he must hide his sin for fear of ignominy and ostracism that damages his soul and body. In his last chapter, Hawthorne states his theme which Dimmesdale has thus demonstrated:
Among many morals which press upon us from the poor minister's miserable experience, we put only this into a sentence: "Be true! Be true! Be true! Sow freely to the world, if not your worst, yet some trait whereby the worst may be inferred!"
I assume you are talking about the final action scene of the novel in chapter 23 - when Dimmesdale climbs the steps of the scaffold in front of everyone during the election day celebration.
Chillingworth runs to him to try to stop him, a final failed attempt in acting like his physician. Dimmesdale at this time is calling to Hester and Pearl - asking them to join him. He dismisses Chillingworth with a clear ambition set hard in his face. Chillingworth realizes by Dimmesdale's determination that he has lost. In Chillingworth's last words to Dimmesdale, he admits his secret evil to the minister and shows what the reader has suspected all along:
“Hadst thou sought the whole earth over...there was no one place so secret—no high place or lowly place, where thou couldst have escaped me—save on this very scaffold!”
Had Dimmesdale only gone public with his sin sooner - he could have escaped the emotional, spiritual and physical torment encouraged by Chillingworth. In one scene - both men admit their final defeat.