And when a Surah is revealed...
"And when a Surah" (from the Quran; it is said that it refers to a specific Surah, which is Bara'ah. Others said the intention is any Surah in which belief and Jihad are mentioned, which is more appropriate and beneficial, because their seeking permission upon the revelation of the verses of Bara'ah is already known from what preceded. Idha (when) implies repetition due to the context, even if it does not strictly imply it by linguistic formation, as some researchers have explicitly stated. It is also permissible that by 'Surah,' a part of it is intended, metaphorically, through the naming of the part for the whole. Al-Kashshaf’s words suggest that applying the term 'Surah' to a part of it is by way of homonymy, like applying the term 'Quran' to a part of it, but that is not substantial). The tanwin (indefinite marking) is for magnification, meaning a Surah of magnificent status.
"That you believe" (meaning: bi-an [in that] you believe; thus an is a verbal particle with the preposition omitted, or it may be explanatory due to the preceding 'revelation,' which contains the meaning of 'speech' without its literal letters). The address is to the hypocrites, and the intent is: "Manifest sincere belief in Allah and strive with His Messenger" (to strengthen His religion and exalt His word). As for generalization, or intending the believers—meaning "continue in belief in Allah, etc.," as Al-Tabarsi and others have suggested—it does not suit the context, and it requires artificial interpretation to connect the condition and the result, which is unnecessary, such as considering the state of the sincere believers within the sublime arrangement.
"They ask your permission" (meaning: they seek your leave). It contains an iltifat (shift in mode of address).
"Those among them who possess wealth" (meaning: the people of virtue and abundance among the hypocrites; they are those who have financial capacity, and physical capacity is known by analogy. They are singled out for mention because they are the ones blameworthy).
"And said: Leave us" (meaning: let us be with those who remain behind).
"With those who sit" (meaning: those who did not strive due to an excuse, among the men and women; hence, the masculine form is used for generalization). The conjunction links to "they ask your permission" by way of explanation, making it unnecessary to mention what they sought permission for, which is the act of sitting behind.