Repetition offers a straightforward example of emphasizing the subject. The first mention reports someone's arrival; the second strengthens that identification.
جَاءَنِي زَيْدٌ زَيْدٌ
Zayd came to me—Zayd himself.
The second «زيد» need not announce a second person or a second arrival. It confirms the first subject expression, especially where the hearer may have misheard the name or been inattentive.