Praise be to Allah.
Al-Quddoos (the Holy) is the One Who is Blessed and Pure, who is exalted above all impurity. It was said that the angels sanctify Him and He, may He be exalted, is the One Who is praised for His virtues and goodness.
Allaah is al-Quddoos because He is far above having any opposites, rivals, partner or son. He is described as being perfect, and is far above having any faults or shortcomings at all. He is far above anything being near Him or like Him in any aspect of His perfection. Ibn Jareer said:
“Taqdees (sanctification) is purification and veneration… Quddoos… purity and veneration are for Him, hence land may be described as ard muqaddasah or holy land, meaning that it is pure. When the angels say ‘Nuqaddisu laka (we sanctify You)’ it means we attribute to You Your attributes of being pure and free of all impurities and of all that the people of kufr attribute to You. It was said that the angels’ sanctification of their Lord is their prayer (salaah). Then he mentioned some of the comments of the mufassireen, who said that taqdees (sanctification) may mean prayer, veneration, glorification, magnification or obedience. Salaah and veneration come back to purification because they declare Him to be pure and free from all that the people of kufr attribute to Him.
Ibn al-Qayyim said:
One of His attributes is the Holy, declaring Him to be above all imperfection and glorifying the Most Merciful