What is the wisdom behind the marriage of the Messenger of Allah's daughters, may Allah bless him and grant him peace, to the sons of Abu Lahab, despite his enmity towards Islam and the disbelief of his two sons?

The daughters of the Messenger of Allah, peace and blessings be upon him, were Zaynab, Ruqayyah, Umm Kulthum, and Fatimah. The Prophet, peace and blessings be upon him, married Ruqayyah and Umm Kulthum to Abu Lahab's sons, Utbah and Utaybah, before the revelation of Surat Al-Masad. After the surah was revealed, Abu Lahab and his wife ordered them to divorce the Prophet's two daughters, so they divorced them before consummation. Uthman ibn Affan married Ruqayyah and she migrated with him to Abyssinia, then she passed away. Then he married Umm Kulthum, and she also passed away.

Marrying a Muslim to a disbeliever and vice versa was not forbidden at the beginning of Islam. It was permissible before the revelation of the verse in Surat Al-Mumtahanah which forbade the marriage of believing women to disbelievers, and the verse in Surat Al-Baqarah which prohibited marrying polytheist women, except for the People of the Book. Therefore, the marriage of Abu Lahab's sons to the Prophet's daughters was common at that time and there was no legal issue with it. Then the divorce occurred before consummation due to Abu Lahab's rage and his insult to the Prophet, peace and blessings be upon him, after the revelation of Surat Al-Masad.