Final answer:
DuBois uses the word 'professes' to convey a stronger connotation and imply insincerity.
Step-by-step explanation:
In the given paragraph, DuBois uses the word professes instead of declares or admits to convey a stronger connotation and emphasize the idea of devotion. The word professes suggests that the slaveholder's profession of Christianity is insincere and implies a negative connotation. It implies that they are pretending or falsely claiming to be Christians.