َ وَاللَّيْلِ إِذْ أَدْبَرَ ﴿۳۳﴾ وَالصُّبْحِ إِذَا أَسْفَرَ ﴿۳۴﴾ إِنَّهَا لَإِحْدَى الْكُبَرِ ﴿۳۵﴾ نَذِيرًا لِلْبَشَرِ ﴿۳۶﴾

﴾33﴿ Wallaili id adbar
﴾34﴿ Wassub hi izaaa asfar
﴾35﴿ Innahaa la ihdal kubar
﴾36﴿ Nazeeral lilbashar

﴾33﴿ And by the night as it turns away
﴾34﴿ And by the morning as it brightens
﴾35﴿ Indeed, this is one of the great matters
﴾36﴿ It terrifies people

[35,36,37] This is the response to the oath: “Indeed, it is” — the pronoun refers to the verses and signs of the Qur’an, just as in the previous pronoun “hiya,” this interpretation applied, and it is fully suitable with the sentences following it. Or the pronoun may refer to Saqar (Hell), or to the denial of the Prophet (May Allah bless him and give him peace), with interpretation as a trait, or it may refer to the Day of Judgment.
“A warner to mankind” — this is a description of the Qur’an and the Messenger, and it can also be a description of the Fire, Saqar, or the Day of Judgment.
“That he may advance” — what is meant is to believe, because that is advancing toward goodness in this world, and in the Hereafter, toward Paradise.
“Or stay behind” — what is meant is disbelief and associating partners (with Allah), which causes one to fall behind from the good of this world and to be deprived of Paradise.
These two types are also mentioned in Surah Al-Hijr (15:24), and this expression of will is mentioned by way of warning, as in Surah Al-Kahf (18:29).