What does "blessing" (niʿmah) refer to here?

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

1. It refers to the Torah with which He entrusted them, and which contains the description of the Prophet Muḥammad ﷺ.[Ibn ʿAbbās]
2. It is what He bestowed upon their forefathers and ancestors when He saved them from the people of Pharaoh, destroyed their enemy, gave them the Torah, and similar favors. [al-Ḥasan, al-Zajjāj]

He reminded them of the blessings He gave to their forefathers because the honour of the forefathers is an honour for their descendants, and the disgrace of the forefathers is a disgrace for their descendants.

1. It is the collection of blessings in various situations. The purpose of mentioning it is to incite gratitude, as whoever does not give thanks has not truly remembered (the blessing).