أَسْعَدُ follows the comparative/superlative pattern أَفْعَلُ. With النَّاسِ, the phrase means “the most fortunate among people.” بِالدُّنْيَا restricts the statement to worldly fortune.
The phrase لَا تَقُومُ السَّاعَةُ حَتَّى... points toward a condition that will occur before the Hour: “not until…”
This grammar supports the central distinction: success in worldly circumstances does not equate to excellence in religion or moral conduct.