Why is this night called Shab Qadr. There are various reasons why it is called so.
First reason: Qadr means greatness and dignity. It has been used in this sense in the following verse of the Holy Quran:
And they (the Jews) did not appreciate Allah with the just estimation that is His true measure. Surah An’aam (6:91)
Allama Abul Hasan ‘Ali bin Muhammad Khazin, (May Allah shower His mercy on him) the author of Tafseer Khazin says:
Translation: This night is called Shab Qadr because of its auspiciousness, majesty and grandeur over other nights. (Lubab Ut Taweel, Surah Qadr-1)
We get to know from this that this night is one of greatness and majesty that is why it is called Shab Qadr.
Second reason: The way this night is one of auspiciousness and excellence, in the same way the good deeds done this night are also accepted and very excellent before Allah Most High. Thus, the good deeds done this night are taken to the door of acceptance by the Momin. It is called “Lailatul Qadr” on this basis as well.
As given in Tafseer Khazin:
Translation: It is called “Qadr” that in this night because of ready acceptance by Allah Most High, the good deeds done by the worshippers have much excellence. (Lubab Ut Taweel, Surah Qadr-1)
Third reason: “Qadr” is also used in the sense of being constrained. It is used in the Holy Quran in this sense:
The affluent should spend (according to) his means. And whoever is provided sustenance scarcely, let him spend (on her maintenance) out of the provision which Allah has given him. Surah At Talaaq (65:7)
This does not mean that this night is a constrained night for the worshippers. In fact, this night angels descend to meet the worshippers of Allah Most High and because of their presence the land is constrained. Thus, the author of Tafseer Khazin writes:
Translation: This night is called “Qadr” because the land becomes constrained because of the coming of angels. (Lubab Ut Taweel, Surah Qadr-1)
Fourth reason: Hadhrat Muhaddith-e-Deccan (May Allah shower His mercy on him) writes yet another reason for called this night as “Qadr”:
Translation: This (night) is called Qadr because the treasured book through the majestic Prophet (Sallallahu alaihi wa sallam) was revealed to the esteemed Ummah. For this reason, “Lailatul Qadr” has been mentioned in the Surah 3 times. (Fadhaail-e-Ramadhan, Surah Qadr-1)
As given in Tafseer Qurtubi, Surah Qadr-1.
To value Shab Qadr and respect it is binding on every Muslim. One way being to truly realize the importance and greatness of Shab Qadr and the other way by busying oneself in worship, remembrance of Allah Most High in this night, and by staying away from the forbidden things.