What is the meaning of "But if they resolve to divorce"?

Imām Ibn al-Jawzī (d. 597/1201) summarized the scholars' opinions in his book "Zād al-Masīr" as follows:

1. When the four months (of īlāʾ) have passed, it becomes obligatory for the man to either reconcile with his wife or divorce her (verbally). [ʿUmar, ʿUthmān, ʿAlī, Ibn ʿUmar, Sahl ibn Saʿd, ʿĀʾishah, Ṭāwūs, Mujāhid, al-Ḥakam, and Abū Ṣāliḥ, who narrated it from twelve other companions. It is also the view of Mālik, Aḥmad, and al-Shāfiʿī]
2. If he does not return to her within the four months, the divorce takes effect without him having to pronounce it. Scholars who hold this view differ on the nature of the divorce: (i) One opinion is that it is an irrevocable (bāʾin) divorce [ʿUthmān, ʿAlī, Ibn ʿUmar, Zayd ibn Thābit, Qubayṣah ibn Dhuʾayb] (ii) The second opinion is that it is a revocable (rajʿī) divorce. [Saʿīd ibn al-Musayyib, Abū Bakr ibn ʿAbd al-Raḥmān, Ibn Shubrumah]