Bismillāh.
فَلَا أُقْسِمُ بِمَوَاقِعِ النُّجُومِ. وَإِنَّهُ لَقَسَمٌ لَّوْ تَعْلَمُونَ عَظِيمٌ. إِنَّهُ لَقُرْآنٌ كَرِيمٌ. فِي كِتَابٍ مَّكْنُونٍ. لَّا يَمَسُّهُ إِلَّا الْمُطَهَّرُونَ. تَنزِيلٌ مِّن رَّبِّ الْعَالَمِينَ
I swear by the places where the stars set! And indeed, it is a great oath, should you know. This is indeed a noble Qur’an, in a guarded Book —no one touches it except the pure ones— sent down gradually from the Lord of all the worlds.
(Sūrat Al-Wāqi‘ah No. 56, Āyāt 75-80)
When we take an oath upon something, its importance must be of an appropriate level relative to that which we are taking an oath for. For example, we would not swear upon a simple pencil to prove our innocence in court, nor would we swear upon our favorite food when trying to display our fidelity to someone. It is expected that the item sworn upon should be of equivalent importance or even more important than the matter being sworn for.
In the above verse, Allah, ‘azza wajall, swears upon “the places where the stars set”. Then He explicitly states in the following verse that this oath is one whose greatness man does not know! In the verse that comes after that, we see that the item which the oath is taken for is the Quran, “This is indeed a noble Quran”. Hence, it follows that the positions of the stars being referred to cannot be as simple as what initially comes to mind.
In the past stars were used to guide someone, to show them the correct path they must traverse. So, Allah subhānahu wata‘ālā uses the means of guidance for people as a thing that He is swearing upon. Moreover, the oath is being taken for the Noble Quran, meaning that this source of guidance should be something of equivalent importance to the Quran. Given all of this, a logical and rational understanding that has been presented by some scholars regarding what Allah (swt) intends by “the place where the stars set” is the Ahl al-Bayt, peace be upon them. They are the source of guidance just like the Quran.
In the verses that follow Allah (swt) goes on to give three very important traits of the Noble Quran, which fit well with the understanding above:
The first item mentioned is that the Quran is “in a guarded Book”. Just as Allah (swt) guarantees protection of the Quran, He also protects the position of guidance of the Ahl al-Bayt ‘alayhimus-salām. It is possible that a wretched individual will burn a copy of the Holy Quran, but the message, the truth and the reality of the Quran can never be eradicated. Similarly, it is possible to martyr the Imams, but the institution of Imāmah can never be eradicated.
The second item is that “no one touches it except the pure ones”. The station of the Quran and the Ahl al-Bayt is one of absolute purity. They are pure since they display nothing but the divine. Only those who are truly pure, those whom Allah has made pure and gives permission to, can hope to meet them. This contact is not physical or apparent; even a disbeliever can touch the Quran or the blessed bodies of the Ahl al-Bayt! Rather, this contact is one where inner self connects to them.
The third and final trait mentioned is that it is something sent down from the Lord of all the worlds. This is also the case for both the Quran and the Ahlul-Bayt. Both have their source in the Lord of the worlds. Both are a revelation brought down to the worldly material realm from a higher immaculate and formless source.
We pray to Allah (swt) to allow us to be pure and attain His proximity by means of both the Quran and the Ahl al-Bayt. We ask Allah to let us recognize that these two means of attaining His proximity will never separate from each other, so we do not fall into excess or deficiency with regards to either one of them.
Sources: Āyatullāh Jawādī Āmulī, Tasnīm; ‘Allāmah Tabātabā’ī, Al-Mīzān.