Evidence and causes for doubt

[Angrboda]

God is light metaphorically in the sense he illuminates and manifests and gives knowledge to others by us seeing him. He manifests the true nature of existence. God being the eternal being that always existed, is the true definition of existence.

You can know it to not be an illusion because your very vision of the soul is borrowing it's existence and luminosity and vision from the source and that what it is manifesting is existence.

Just like you can see you yourself exist, God manifests the truest form of existence. Not only that, it's manifest if you look and reflect over what you are seeing when seeing both him and creation, is that creation get's defined from with respect to it's reality from the source. Everything is created in truth. Everything is created by reality of God. 

God manifests what is real, what is truly exists. What you imagine of matter or quarks existing on it's own, is nothing but conjecture, and you don't know any of this to be what truly exists on it's own.

God is the manifestation of true existence. He is the life by which all life exists. He is the blessed one in the blessings.

By being light, God manifests through light, in various degrees, in various hues, states that are linked to him.

Seeing his light may start off with nothing but a distant star. If God shines even as a distant star, you must believe that is your Lord.

As trust and confidence grows, so does the light and luminosity. In fact, these things are linked.  And so is the love with power. 

With love of God one can see the true nature of existence and power of vision grows as love and attachment to God grows.