What usage does the book illustrate with “thumma kana min alladhina amanu”?

Particles of Meaning: Waw, Fa, Thumma, Bal and Lakin

• Thumma may contextually carry a joining sense resembling waw
• Thumma necessarily marks literal delay, making faith chronologically last
• Thumma corrects the preceding statement as bal would
• Thumma negates all prior actions and affirms the later one