Tafsir of Ash-Shura 42:39

This means they take vengeance upon those who have committed tyranny against them, in accordance with what Allah, the Exalted, has permitted for them, and they do not transgress.

The significance of the specification here is that they are the ones specifically characterized by defending themselves, while others remain subservient. It is not intended that they defend themselves and do not forgive, for that would contradict the preceding verse. Rather, He, the Glorified, has described them as being specifically characterized by forgiveness—such that anger does not overpower their intellects as it does others—and as being specifically characterized by defense—to the extent permitted for them if they retaliate—without transgressing as others do. Thus, they are praiseworthy in both states: between good and better, distinguished by this above all other people.

Many have said: Each of the two descriptions has its proper place where it is praiseworthy. Forgiveness is praiseworthy when dealing with one who is unable to resist and admits his guilt, and the word "forgiveness" (maghfirah) implies this. Defending oneself is praiseworthy when dealing with a stubborn adversary, and the word "defense" (intisar) implies this. If one were to act in the opposite manner in these situations, both would be blameworthy. It is in this sense that the saying goes: "If you honor the noble, you own him; but if you honor the base, he rebels." Applying mercy where the sword is required is just as harmful to nobility as applying the sword where mercy is required. It is also possible that each is praiseworthy or blameworthy based on other considerations, so there is no contradiction, regardless of whether the one described in both sentences is the same or not.

Some scholars have said: The most appropriate approach is not to interpret the speech as a specialization, but rather as one of piety. That is, they practice forgiveness at times and defense at others, not constantly, to avoid contradiction—though this view is not particularly strong.

It is reported from al-Nakha'i that when he read this verse, he would say: "They used to dislike humbling themselves, lest the corrupt be emboldened against them." This implies that defending oneself is intended for the stubborn adversary; otherwise, there is no humiliation of the self in forgiving one who is weak and acknowledges his fault.

As for the sentence {they defend themselves}, it consists of the subject and predicate, acting as the relative clause for the pronoun "those who" (al-ladhina), with "when" (idha) serving as the adverb for "they defend" (yantasirun). It is also permissible to consider "when" (idha) as conditional, with the sentence being the response to the condition, and the combination of the condition and its response serving as the relative clause. Abu Hayyan critiqued this with what was mentioned earlier. It is also permissible to consider "they" (hum) as the subject of a deleted verb, similar to what you heard regarding the verse {And when they are angry...}. Al-Hawfi said: It is permissible to consider "they" (hum) as an emphatic reinforcement for the pronoun in {strikes them} (asabahu), though this involves separating the emphasizer and the emphasized with the subject—yet it is not impossible. Nevertheless, the preferred grammatical analysis is what we pointed out first.