What is meant by "repelling people by means of each other"?

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

1. It means: were it not the case that Allah (in His wisdom) repels those who disobey Him by those those who obey Him — as He repelled those who disobeyed Saul by those who obeyed him — then the disobedient would have perished swiftly by punishment. [Mujāhid]
2. It means: were it not for Allah restraining the polytheists by the Muslims, the polytheists would have prevailed over the land, killed the Muslims, and destroyed the mosques. [Muqātil]