Muhammad said: Meaning, Allah gave David [this], because he was made king after he killed Goliath. "And He taught him of that which He willed," meaning: the revelation that used to come to him from Allah. "And were it not for Allah checking some people by means of others, the earth would have been corrupted." Qatada's interpretation: The believer is tested by the disbeliever, and the disbeliever is spared by the believer.

Muhammad said: It is said the meaning is: Were it not for Allah's checking of the disbelievers by means of the Muslims, disbelief would have increased, and therefore the wrath would have descended upon the people, and the inhabitants of the earth would have been utterly destroyed. "Some of them" (ba'dahum) is in the accusative case as a substitute (badal) for "the people" (al-nas); the meaning is: Were it not for Allah's checking of some people by means of others.