The Quran

وَما جَعَلنا أَصحابَ النّارِ إِلّا مَلائِكَةً ۙ وَما جَعَلنا عِدَّتَهُم إِلّا فِتنَةً لِلَّذينَ كَفَروا لِيَستَيقِنَ الَّذينَ أوتُوا الكِتابَ وَيَزدادَ الَّذينَ آمَنوا إيمانًا ۙ وَلا يَرتابَ الَّذينَ أوتُوا الكِتابَ وَالمُؤمِنونَ ۙ وَلِيَقولَ الَّذينَ في قُلوبِهِم مَرَضٌ وَالكافِرونَ ماذا أَرادَ اللَّهُ بِهٰذا مَثَلًا ۚ كَذٰلِكَ يُضِلُّ اللَّهُ مَن يَشاءُ وَيَهدي مَن يَشاءُ ۚ وَما يَعلَمُ جُنودَ رَبِّكَ إِلّا هُوَ ۚ وَما هِيَ إِلّا ذِكرىٰ لِلبَشَرِ

Muhammad Asad

For We have caused none but angelic powers to lord over the fire [of hell];¹ and We have not caused their number to be aught but a trial for those who are bent on denying the truth² - to the end that they who have been granted revelation aforetime might be convinced [of the truth of this divine writ];³ and that they who have attained to faith [in it] might grow yet more firm in their faith; and that [both] they who have been granted the earlier revelation and they who believe [in this one] might be freed of all doubt; and that they in whose hearts is disease⁴ and the who deny the truth outright might ask, "What does [your] God mean by this parable?"⁵ In this way God lets go astray him that wills [to go astray], and guides aright him that wills [to be guided].⁶ And none can comprehend thy Sustainers forces save Him alone: and all this⁷ is but a reminder to mortal man.

Since it is by virtue of his powers of conscious perception and conceptual thinking that man can arrive at a discriminating cognition of good and evil and, thus, rise to great spiritual heights, these powers are described here as "angelic" (lit., "angels" - this being the earliest occurrence of the term malak in the history of Qur'anic revelation). On the other hand, since a neglect or a deliberately wrong use of these angelic powers is at the root of all sinning on the part of man and, therefore, of his suffering in the hereafter, they are spoken of as "the lords (ashab) of the fire [of hell]", which complements the expression "over it"' in the preceding verse.
This is apparently an allusion to the allegorical character of this passage, which "those who are bent on denying the truth" are unwilling to recognize as such and, hence, fail to grasp its real purport. By speculating on the reasons which allegedly induced Muhammad - whom they regard as the "author" of the Qur'an - to lay ~tress on one particular number, they tend to take the allegory in a literal sense, thus missing its point entirely.
Namely, by being enabled, through an understanding of the above allegory, to appreciate the rational approach of the Qur'an to all questions of faith. The reference to "those who have been granted revelation aforetime is the earliest statement outlining the principle of continuity in mankind's religious experience.
I.e., in this instance, the half-hearted ones who, despite their ability to discern between right and wrong, incline towards unbelief.
Cf. the identical phrase in 2:26, together with the corresponding note 18. My interpolation, in both these passages, of the word "your" between brackets is necessitated by the fact that it is the unbelievers who ask this question.
Or: "God lets go astray whomever He wills, and guides aright whomever He wills" (see surah 14, note 4). The stress on the allegorical nature of the above passage, spoken of as a "parable" (mathal), has here the same purpose as in 2:26 - namely, to prevent the followers of the Qur'an from attaching a literal meaning to its eschatological descriptions - a purpose that is unmistakably expressed in the concluding sentence of this passage: "All this is but a reminder to mortal man". (See also next note.)
Lit., "it" or "these" - depending on whether the personal pronoun hiya is taken to denote a singular - in which case it would refer to the feminine noun saqar, "hell-fire" (Tabari, Zamakhshari, Baghawi, Ibn Kathir) - or a plural, referring to what Razi pinpoints as "those [Qur'anic] verses dealing with these allegories (hadhihi 'l-mutashabihat)": hence my compromise rendering "all this".