After Allah (swt) explains the things related to The Day of Judgment, He (swt) begins this Surah by swearing. Allah (swt) swears by whatever He Wills regarding whatever He Wills. As such, Allah (swt) swears by His Messenger (saws):

 ﴾لَعَمْرُكَ إِنَّهُمْ لَفِي سَكْرَتِهِمْ يَعْمَهُون ﴿

(Verily, by your life (O Muhammad ), in their wild intoxication, they were wandering blindly.) (Al-Hijr: 72)

He also swears by time, such as in this verse:

﴾ وَالْعَصْر إِنَّ الإِنسَانَ لَفِي خُسْر﴿

(By Al-‘Asr (the time) % Verily! Man is in loss) (Al-‘Asr: 1-2)

He swears also by the sun, moon and many other signs of the universe that He Wills to draw the attention of human beings to.

So here, Allah (swt) swears by 5 things which are in fact unknown to mankind, as they are connected to matters of the unseen. The scholars have also differed in their interpretations. Most of the exegetes (Scholars of Tafsir) are of the opinion that are concerning the angels and their tasks: