Final answer:
Abraham Lincoln was chosen as the Republican candidate over William H. Seward because of his reputation as a moderate, his relatable background, and his representation of the crucial state of Illinois.
Step-by-step explanation:
During the Republican convention in 1860, the leading contenders for the nomination included Abraham Lincoln, William H. Seward, Salmon P. Chase, Simon Cameron, and Edward Bates. While Seward appeared strong initially, the party leaders hoped to nominate a candidate who could help in weaker states. Many voters linked Seward with radical abolitionist sentiments due to his 'Higher Law' speech. Ultimately, three factors worked in Lincoln's favor: his reputation as a moderate, his relatable background, and his representation of the crucial state of Illinois.