﴾48﴿ Qaalal lazeenas takbarooo innaa kullun feehaaa innal laaha qad hakama baynal'ibaad
﴾49﴿ Wa qaalal lazeena fin Naari likhazanati Jahannamad-'oo Rabbakum yukhaffif 'annaa yawmam minal 'azaab
﴾50﴿ Qaalooo awalam taku taateekum Rusulukum bilbaiyinaati qaaloo balaa' qaaloo fad'oo; wa maa du'aaa'ul kaafireena illaa fee dalaal
﴾51﴿ Innaa lanansuru Rusulanaa wallazeena aamanoo fil hayaatid dunyaa wa Yawma yaqoomul ashhaad

﴾48﴿ And those who were arrogant will say, "Surely, we have all fallen into this. Surely, Allah, the Exalted, has decided between His servants
﴾49﴿ And those who are in the Fire will say to the keepers of Hell, Pray to your Lord to lighten for us the punishment for one day
﴾50﴿ They will say, Did your messengers not come to you with clear proofs?" They will reply, "Yes, indeed." The angels will say, "Then pray for yourselves. But the prayer of the disbelievers is nothing but in vain
﴾51﴿ Surely, We help Our messengers and the believers in the life of this world and on the Day when the witnesses will stand forth

[48] This is the response of the arrogant leaders (mustakbirīn), expressing their helplessness — meaning: “We cannot even save ourselves, so how could we possibly protect you from the punishment?”
It is a clear admission of defeat and inability to offer any benefit or protection.
[49] When they lose hope in helping one another among themselves, they will then turn to the keepers of Hell (the angels) and ask them to pray on their behalf.
This reflects their desperation and realization that no intercession or escape remains for them.
[50] This is the angels’ response, given with emphasis and rebuke.
(And the supplication of the disbelievers is only in vain) — this refers specifically to their supplications in the Hereafter, which are completely futile and will not be accepted.
In contrast, some of their supplications in the world may be accepted, due to divine wisdom or as a test, but in the Hereafter, such calls hold no value.
[51] The third section of this surah, which continues until the end, offers consolation to the believers, commanding the caller to:
Be patient, Engage in seeking forgiveness (istighfār), Glorify (tasbīḥ) Allah, And seek refuge (isti‘ādhah) during disputes with the people.
Then comes affirmation of the Resurrection with two rational proofs.
After that, there is once again a refutation of shirk in supplication (shirk fī al-du‘ā) — which is the central theme of the surah — followed by seven detailed proofs. In these proofs, Allah’s blessings are listed in detail, and it is shown that Allah alone is the Owner of all these favors — so why ask others for your needs?
Then comes severe warning and rebuke for those who argue (against the truth), and a summary historical proof from the stories of the Prophets (peace be upon them).
Following that are three rational arguments, and the section concludes with: A worldly warning, And a statement that repentance will no longer be accepted at the time of punishment.
In verse (51), there is consolation through the promise of divine help, which is the final outcome referenced earlier:
That Pharaoh and his people were afflicted with punishment in both this world and the next, while Allah the Exalted saved the believing Israelites and aided them against their enemy.
This is the case for all true believers.
(The witnesses — الأشهاد) refers to those mentioned in various other verses as witnesses:
The Prophets, as in Surah An-Nisā’ (41), The believers, as in Surah Al-Baqarah (143), The body parts, as in Surah Yā Sīn (65), An-Nūr (24), and Ḥā Mīm As-Sajdah (20), The angels, as in Surah Qāf (21).