Ma nunazzilu almala-ikata illa bilhaqqi wama kanoo ithan munthareen (surah Hijr: 8)

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(15:8) We do not send down angels in this way. When they come down, *4 they come down with truth, and then the people are not given respite. *5

Maa nunazzilul malaaa`i kata illaa bilhaqqi wa maa kaanooo izam munzareen

*4) This was a sarcastic remark that was made by the opponents, for they did not acknowledge that the "Admonition" had been sent down to the Holy Prophet: otherwise they could not say that he was "insane". What they really meant by this remark was: "You, who claim that the "Admonition" has been sent down to you, are insane". A similar remark was also made by Pharaoh concerning Prophet Moses. Addressing his courtiers, he said, "The Messenger who has been sent to you is insane". (XXVI: 27)
*5) "We do not send down the angels in this way": We do not send down the angels for the mere fun of it in response to the request of the people: nor are they sent to unveil the Reality before them in order to show to them all the "unseen" things to which the Messengers invite them to believe. As a matter of fact, angels are sent down on that occasion when it is decreed to pass judgment on sane wicked people. At that time the judgment comes into operation without extending. any invitation to the condemned people to accept the Message, for their period of respite ends as soon as the "Reality" is unveiled before them.
"......they come down with truth": "......they bring down truth with them" . That is they come down to eradicate falsehood and to establish truth in its stead. Or, in other words, it means, .....they come down to put into force the judgment of Allah".