From Surah Nur, Explanation from Maariful Quran and Ibn Kathir
Allah is the Light of the heavens and the earth. The parable of His Light is as (if there were) a niche and within it a lamp, the lamp is in glass, the glass as it were a brilliant star, lit from a blessed tree, an olive, neither of the east (i.e. neither it gets sun-rays only in the morning) nor of the west (i.e. nor it gets sun-rays only in the afternoon, but it is exposed to the sun all day long), whose oil would almost glow forth (of itself), though no fire touched it. Light upon Light! Allah guides to His Light whom He wills. And Allah sets forth parables for mankind, and Allah is All-Knower of everything.Commentary:WHAT IS MEANT BY NUR HERE? Nur is in fact that condition which is initially perceived by man's sense of sight, and then through that perception he comprehends all those things which can be seen by eye, such as in the case of rays of sun and the moon, which on falling on a solid mass brightens it up, and then through the reflection from solid mass brightens other things.
Hence, it is evident that the word Nur cannot be used for Allah SWT in its literal or common meaning, because He is free from body and materiality. Therefore, there is consensus among the scholars that the use of word Nur for Allah SWT in the verse under reference is purported for Munawwir, meaning the one who brightens, or may be the master of brightening is referred here as Nur, in the same way as the possessor of grace is sometimes called Grace, or the possessor of justice is called the Justice. So, meaning of the verse is that Allah bestows Nur to earth and the heaven, and to everything living there, and the Nur is purported to be the Nur of righteousness.
The example of His light is that of a niche in which there is a lampThis is a nice example of Allah SWT’s Nur of guidance, which penetrates into the heart of the believer.-
It means that this is the example of the believer in whose heart Allah SWT has laid down the Nur of faith and of the Quran. In this verse Allah has first mentioned His own Nur, and then the Nur of the believer's heart-and the following example is for the one who believes in Him.
'Masalu noorihi- The parable of His Light' Two interpretations:1.This pronoun has reference toward Allah SWT, and thus the meaning of the verse is 'Allah's Nur placed in the heart of believers naturally', and the example of that is kamishkatin (like a niche). This explanation is put forward by Ibn Abbas .
2. The other explanation is that the personal pronoun refers to the believers, who are presumed to have been referred to by the context.
So, the example given in the verse can be explained as follows:
The chest of a believer is like a niche, while the heart of the believer placed in the chest is like a lamp (placed in the niche). Then the transparent oil of olive is the example of the natural nur (light) of guidance which is deposited in the nature of a believer and which has the inherent capability to accept the truth (which is indicated in the verse by the words 'Its oil is about to emit light even if fire has not touched it).
Then as the olive oil produces brightness when caused to burn with the flame of fire, the same way natural Nur of guidance which is placed in the heart of the believer, when joins the message and knowledge of Allah SWT, then it gets brightened and also brightens the world.~*~
When the companions and their pupils confined this example to the heart of a believer alone, they have most probably done so because it is only the believer who draws benefit from this Nur. Otherwise the natural Nur of guidance which is placed in the hearts of humans at the time of their creation, is not confined to believers, but is part of the nature and instinct of every human being.
It is for this reason that one can see all around the world that there are people in every nook and corner, in all societies and religions, who believe in the existence of God and His Omnipotence, and do turn towards Him. No matter one may make all types of errors in the perception and understanding of God, yet every individual does believe by nature in His existence, with the exception of a few atheists, who have who have lost their natural instinct.
'Every child is born with natural instinct'. Later, his parents put him on the wrong path. This natural instinct is the guidance of faith. The guidance of faith and its Nur is bestowed to every individual at the time of his birth, and because of this Nur of guidance, one possesses the ability to accept the truth. When they come to know about the revelations of Allah through His messengers and their deputies, they readily accept them, except those unfortunate people who have erased the Divine Nur
from their heart with their wrong doings.
Perhaps this is the reason that in the beginning of the verse the bestowal of Nur is said to be common to all, which includes every one on the earth and the heavens, without any difference between believers or disbelievers, but towards the end of the verse it is said 'Allah guides to His light whomsoever He wills - 35'. Here the will of Allah is not pointing toward that Divine Nur which is bestowed to all humans, but toward the Quranic Nur, which is not availed by every one, except those fortunate ones, to whom Divine help is granted. Otherwise even one's endeavor goes waste without Divine help, and sometimes becomes detrimental :
‘ If there is no help to man from Allah, then his striving puts him to trouble instead'.Another interpretation is that:This example was meant for the heart of the Holy Prophet sallalahu alayhi wassalam. the niche stands for his chest, Zujajah (glass) for his heart and Misbah( lamp) for his prophethood. What was unique about this Nur of prophethood was that even before the declaration of prophethood it had the illumination of light for the people. When the revelation from Allah is coupled with the Nur of prophethood, then it turns into such radiance that the whole world is brightened.
Before the declaration of prophethood of the Holy Prophet, and even before his birth, some strange and amazing events had taken place in the world, which were in fact advance notice of the incoming prophet, and are called Irhasat in the vocabulary of the scholars of hadith. The difference between this word and miracle is that the latter is used for such unusual events which are bestowed by Allah SWT to his messengers for the endorsement of their prophethood, while Irhasat are those unusual events which happen before the declaration of prophethood. There are a number of unusual incidents which are recorded by several authentic narrations, and have been compiled by Shaikh Jalaluddin Sapti in his book Khasais Kubra - and by Abu Nu'aim in his Dalail-un-Nubuwwah. Other scholars have also collected many such incidents in their books. Tafsir Mazhari has reproduced a good number of these events.
Thus Allah SWT gave a unique example of placing His Nur of guidance in the heart of believers. Toward the end of the verse it was clarified that only those draw benefit from this Nur, whom Allah loves and grants Divine help.
Neither of the east nor of the west "This is a tree in the desert which is not shaded by any other tree or mountain or cave, nothing covers it, and this is best for its oil.'' Mujahid commented on:
Neither of the east nor west..
"It is not in the east where it will get no sun when the sun sets, nor is it in the west where it will get no sun when the sun rises, but it is in a position where it will get sun both at sunrise and sunset.'' Sa`id bin Jubayr commented:
An olive, neither of the east nor of the west, whose oil would almost glow forth (of itself)) "This is the best kind of oil. When the sun rises it reaches the tree from the east and when it sets it reaches it from the west, so the sun reaches it morning and evening, so it is not counted as being in the east or in the west.''
Noorun ala Noor, Light upon LightAl-`Awfi narrated from Ibn `Abbas that this meant the faith and deeds of a person. As-Suddi said:
(Light upon Light!) "Light of the fire and the light of the oil: when they are combined they give light, and neither of them can give light without the other. Similarly the light of the Qur'an and the light of faith give light when they are combined, and neither can do so without the other.''
Allah SWT guides to His Light whom He wills(Allah guides to His Light whom He wills.) means, Allah shows the way to the ones whom He chooses, as it says in the Hadith recorded by Imam Ahmad from `Abdullah bin `Amr, who said, "I heard the Messenger of Allah say:
Allah created His creation in darkness, then on the same day He sent His Light upon them. Whoever was touched by His Light on that day will be guided and whoever was missed will be led astray. Hence I say: the pens have dried in accordance with the knowledge of Allah, may He be glorified.''
Olive OilThis is an endorsement that olive and its tree is blessed by Allah and is beneficial and useful.
Scholars have commented that Allah SWT has instilled many a benefits in it. Olive oil is used in the burning of lamps. Its light is the brightest and clearest as against any other oil. It is eaten as a fruit and its oil is used in cooking. The interesting part is that there is no need of any machine for the extraction of its oil. When the fruit is ripe, the oil comes out automatically. The Holy Prophet sallahu alayhi wassalam has asked to eat and massage the body with olive oil.
On a last note, The Messenger pbuh is reported to have said:Hearts are of four kinds: the heart that is clear like a shining lamp; the heart that is covered and tied up; the heart that is upside-down; and the heart that is clad in armor.
As for the clear heart, it is the heart of the believer in which is a lamp filled with light; as for the covered heart, this is the heart of the disbeliever; as for the upside-down heart, this is the heart of the hypocrite, who recognizes then denies; as for the armor-clad heart, this is the heart in which there is both faith and hypocrisy.
The parable of the faith in it is that of legume, a sprout that is irrigated with good water, and the likeness of the hypocrisy in it is that of sores that are fed by blood and pus. Whichever of the two prevails is the characteristic that will dominate
And Allah SWT knows best. 
(Ibn Kathir on this ayah:
www.islam-universe.com/tafsir_ibn_kathir/24.35990.html )
