Psalm 23, one of our most famous scripture speaks of the "Valley of the shadow of death" and again in Hebrews 10 we are taught the law is only a shadow of the real thing. That is shadows are merely a reflection of what is true but in themselves are not truth.
When I sit in my garden at home, one of the most appealing and beautiful aspects of it is the shadows that the trees and their leaves cast around the place. Their reflections in themselves can be quiet amazing and beautiful. To cast a shadow it is imperative that two elements are present, one that there is light and two there is also darkness, for without one or the other shadows are not possible.
When we consider the garden of our lives shadows play a very important role. Just as believers and followers of Christ we want God's light to be present and endearing it is also important that we have darkness to reflect or cast shadows to show us what could be. This in no way means we want darkness present in our lives but are still able to understand that the presence of darkness in the world in which we live also provides the "children of light" with a reflection or understanding of its effects.
In the garden of Eden were many trees but only one tree was forbidden to eat from. The absence of this tree would have not given man the opportunity to rebel from God and therefore understand their potential for evil and therefore a free will to serve God or not. Darkness in the world therefore gives us not only the option to pursue light and all it entails but also to see the effects of darkness around us.
When we become angry and do things we regret which I have done many times in my life, I am able to see the effects of darkness in my life and it gives me an option to rid myself of it and change. Obviously I cannot merely change my reaction or angry behaviour without first dealing with the true cause of my anger but because of this behaviour I am then able to pursue what is good and right for my life. Scripture calls this the "higher way" and it speaks of God's work of transformation in our lives to become the "pure and spotless bride" that Christ so desires.
God bless you in your desires to seek first God's kingdom and His righteousness