What is meant by "strength" (quwwah) in this āyah?

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

1. Earnestness and diligence. [Ibn ʿAbbās, Qatādah, al-Suddī]
2. Obedience. [Abū al-ʿĀliyah]
3. Acting on its teachings. [Mujāhid]
4. Sincerity. [Ibn Zayd]