Final answer:
Chillingworth aims to prevent Dimmesdale's confession to maintain his hold over the minister and continue his vengeful satisfaction. A confession would grant Dimmesdale redemption and nullify Chillingworth's influence, which is not only his revenge but his sole purpose.
Step-by-step explanation:
Chillingworth desperately tries to stop Dimmesdale from confessing his sins on the scaffold because doing so would rob Chillingworth of his purpose. For Chillingworth, Dimmesdale's torment is not just revenge but also a source of empowerment.
Chillingworth has dedicated his life to psychologically manipulating and controlling Dimmesdale, which is his form of retribution for Dimmesdale's affair with his wife, Hester Prynne. If Dimmesdale confesses, he would free himself from Chillingworth's grip, thus negating Chillingworth's influence and satisfaction over his enemy.
The act of confession would also offer Dimmesdale a chance at redemption and peace, something Chillingworth does not want. Ultimately, Chillingworth's obsession with revenge becomes his own downfall, as it consumes his identity and purpose.