Example 1: “A man came” gives no particular identification; “the man came” presupposes a recoverable referent; “Zayd came” identifies by proper name; “Zayd’s brother came” identifies through annexation.
Example 2: «مَا جَاءَنَا مِنْ بَشِيرٍ» uses indefiniteness under negation to exclude all relevant individuals, whereas «الرسول» can point to a messenger previously mentioned. Sound analysis requires form, referent, and communicative purpose together.