Final answer:
Douglass achieves emphasis and contrast with the repetition of the words 'loyal' and 'rebel' to stress the loyalty of African Americans during the Civil War and challenge stereotypes.
Step-by-step explanation:
Douglass achieves the effect of emphasis and contrast with his repetition of the words loyal and rebel in this excerpt. By repeating these words, Douglass is stressing the key concept that African Americans were loyal to the Union cause during the Civil War, while their masters were rebels and traitors. The repetition highlights the stark contrast between the actions and character of African Americans and their white masters. The possible impact on the audience is to challenge their preconceived notions about African Americans and undermine the stereotype of African Americans as ignorant and disloyal.