"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 enclosed in glass,
the glass shining like a radiant star:
lit from a blessed tree -
an olive tree neither of the East nor of the West -
whose oil would almost give light (of itself) even though it had not been touched by fire.

Light upon Light!

'Allah guides whom He will to His Light.'

'Allah doth set forth Parables for men: and Allah doth know all things.' [The Holy Quran, 24:35]

Ubayy ibn Ka`b[ra] said:-

'The similitude of His light [takes place in] the Muslim's heart.'

This light, which He has placed in the heart -- love, faith and the remembrance of God. It is the light that He has sent down to His servants, by which He gives them life, and by which they walk among people. Its origin is in their hearts, but then He strengthens and increases it until it appears upon their faces, limbs, bodies, even their clothes and dwellings.

People of this nature perceive it, while others deny it.

On the Day of Judgement, however, it will come forth by their faith, and hasten before them in the darkness of the Bridge, that they might cross it.

They will proceed in proportion to either its strength or its weakness in their hearts during their life in the world.[Ibn Kathir, 3:464]