How are we to understand His name Al-Nur, The Light?
Ibn 'Abbas said, "Light refers to guidance for those in the heavens and earth from falsehood to truth" (Tafsir al-Tabari 18:135).
Light and darkness also apply to the realm of meaning. Light is that which removes the darkness of ignorance and falsehood. Al-Ghazali says, the layers of darkness are non-existence, ignorance, and misguidance. Being Al-Nur is being free from all of these darknesses absolutely and by necessity, without having to have made an effort nor relief upon an aid. The name Al-Nur is also that He is the source of guidance out of darkness.
Why can't Allah be physical?
Response: In Surat al-Ikhlas He described Himself as Ahad, which is one in Himself, i.e. indivisible. Matter is anything that takes up space, which means it must be divisible, having a top and a bottom, a right and a left, while Allah is not divisible. Further, anything material is limited to its mass and dependent upon space, and Allah is neither limited or dependent (Allahu al-Samad).
Why is it impossible for Allah to descend into the creation or come in the form of something?
1 It implies the existence of a location outside of creation.
The very nature of entering into the creation implies that He was originally located outside of it, which is impossible because there is no location outside of creation. There is only pure nothingness, which the human mind cannot fathom.
2 It requires that Allah's essences is physical.
Entering creation implies the movement of God's essence. Movement implies physicality, since only physical things can move. Non-physical things, like ideas or thoughts, cannot move.
3 it requires that Allah be limited and contained.
If Allah were to enter the universe, He would need to be inside of something, such as a body, or smoke, or light. This would mean that Allah is contained, whereas He is the Limitless. (Even light is composed of tiny particles of matter, the proof of which is that it refracts.)
4 It would require dependency.
He would be dependent upon whatever body He came in, whereas He is Al-Samad, the Absolutely Independent.