COMMENTARY on 39:16
A. Yusuf Ali:

Translation:
They shall have Layers 4266 of Fire above them, and Layers (of Fire) below them: with this do Allah warn off 4267 his servants: "O My Servants! then fear you Me!"
Commentary:

4266  The consequences of Sin when Judgement comes are aptly figured by Layers upon Layers of Fire, which hem in the sinners above and below. It is also suggested that the Layers, though of Fire, have something dark in them—the scorching quality of Sin.

4267  But Allah does not leave mankind without warning. Man has been granted a limited amount of free will, and in order to help him in its right use, all the consequences of his action are clearly explained to him. To those who will listen to Reason are given arguments which can be apprehended by their own intelligence; to those who are swayed by affections and emotions, an appeal is made in the name of the Love of Allah; to those who understand nothing but fear, the warning is conveyed by a portrayal of the dreadful consequences of wrongdoing,

 

Muhammad Asad:

Translation:
Clouds of fire will they have above them, and [similar] clouds beneath them…” In this way does God imbue His servants with fear. 19 O you servants of Mine! Be, then, conscious of Me -
Commentary:
19  As in many other instances, the Qur’an alludes in this phrase to the allegorical nature as well as to the real purpose of all descriptions of the suffering which awaits the sinners in the hereafter; cf. 74:35-36 - "that [hell-fire] is indeed one of the great [forewarnings]: a warning to mortal man".