جَاءَ الرَّجُلُ الْعَالِمُ — adjective: a quality.
جَاءَ زَيْدٌ نَفْسُهُ — emphasis: the very person.
جَاءَ أَخُوكَ خَالِدٌ — explanatory apposition: identity.
جَاءَنِي أَخُوكَ زَيْدٌ — a badal analysis is possible when Zayd is the primary intended participant.
Identify a follower by its semantic work, not only the case ending.