Tafsir of Al-Hujurat 49:15

(The believers are only those who have believed in Allah and His Messenger, and then did not doubt)—that is, they did not waver. The word irtaba (to doubt) is the derivative form of rābahu, meaning to cause someone to fall into doubt mixed with suspicion. The lack of doubt is mentioned as being subsequent to the initial belief, despite the fact that belief cannot be separated from the absence of doubt. This is to convey the negation of doubt even after the occurrence of a شبهة (misgiving or doubt-inducing situation). It is as if it were said: "They believed, and then they were not afflicted by what afflicts the weak after a time." This does not indicate that they were doubtful at first; rather, it indicates that just as they did not doubt initially, no doubt arose in them subsequently. The conclusion is: they believed, and then no doubt occurred to them; thus, the sequence is temporal.

Some eminent scholars have said: Coordinating the lack of doubt with belief is like the phrasing ("His angels and Gabriel"), intended to alert that [lack of doubt] is the core of belief, as if it were something distinct and higher residing within it. The word thumma (then) was preferred over wa (and) to indicate that this core [of certainty], in its strength and stability, is the same in its initial state as it is in its enduring state; it is always fresh, rather than being a single, continuous thing that remains unchanged, like something created [in the past]. Instead, it is renewed and fresh from time to time. There is no harm in considering this a reinforcement of what the meaning of the coordination implies. Since it was made distinct, it alerts us that this is not the distinction between persistence and occurrence, but the distinction between two different things, in order to indicate the aforementioned meaning: that they are in an increase of certainty moment by moment. As for those who hold that belief fluctuates in strength and weakness, this is self-evident. As for those who do not hold this view, [it is explained by] the addition of direct observation (’iyan) to evidentiary proof (bayan).

The difference between the two types of persistence is that, in the first case, persistence refers to the whole, as in the saying of the Almighty: "They said, 'Our Lord is Allah,' and then they remained steadfast"—meaning their belief remained constant with the absence of doubt. In the second case, persistence is considered with respect to the final part [of the sequence]. This interpretation is more sound. In any case, the speech contains an insinuation against those Bedouins.

(And who strive with their wealth and their lives in the cause of Allah)—in His obedience, Majestic and Exalted be He, in its various forms: physical worship alone, financial worship alone, and those that combine both, such as Hajj and Jihad. Placing wealth before the soul is a form of progression from the lesser to the greater. It is also permissible to say: wealth was mentioned first because of the intense attachment many have to it, to the point that they would destroy their own souls for its sake. This is also more fitting with respect to the insinuation against those [Bedouins], since it was not enough that they did not strive with their wealth; they even came and displayed Islam out of a desire for spoils and the vanities of this world. The meaning of "strove" (jahadu) is that they exerted their effort, or its object is implied—that is, the enemy, or the self and desire.

(Those)—described by the beautiful attributes mentioned—(are the truthful)—that is, those who are truthful in their claim of belief, not those Bedouins. It is narrated that when the verse was revealed, they came and swore that they were truthful believers, so the Almighty’s saying was revealed to belie them: [The rest of the verse].