In any explorations of the world of form, even within the utterly simple context of all as Spirit, it quickly gets very complex - infinitely complex.
The whole topic of the fertile darkness, and it symbolisms and archetypes of the dark goddesses, is one example of this. There is so much here, explored to far more detail and from far more experience and clarity than I can bring to it, but here is a simple overview of what comes to mind right now.
First, there is the projection and shadow aspect.
Consequences of the split: covering up the ground
If the world of form is split into good and bad, and the division is seen as real and important, the drama will hinder us in recognizing the ground that is always there. The fascination with the drama itself distracts us from noticing the ground. The dust kicked up in the drama of pushing some aspects of form away and holding onto other aspects, covers up the ground.
It covers up the Ground of seeing and seen, it covers up the fertile dark ground of form, and it covers up the inherent absence of an I anywhere in these grounds and all form.
Inner and outer consequences of the split
In our western culture, we associate light with good and dark with bad (or evil). Light is used to describe the light of consciousness, of what is known, of the divine, the masculine, mind, heaven, civilization, technology, purity, truth. Darkness is used to describe the opposites, including the unknown, the feminine, the body, the earth, nature, the uncivilized - all seen as less desirable.
We all know what this meant at our collective level: men, (western) civilization, technology, mind, the known and purity is elevated and gain power, while women, non-white, non-western cultures, nature, the body and the unknown have been seen as defiled, less valuable, and is excluded from influence.
The same split is of course right here as well, at our individual levels: we value the mind as a source of information and less so the body, we want to be right not wrong, we want knowing not not-knowing, and so on.
As with life in general, at whatever level we look, the pendulum eventually swings back. So now, there is a growing appreciation of most of what was left out: non-western cultures, non-whites, women, the feminine, the earth, the body, and even - in some circles, not knowing.
A good examples is the flourishing of Wiccans who explicitly include women, the feminine, the goddesses, the Earth and the bodies. Within traditional religions, there is a similar shift, for instance seen in the renewed interest in the Black Madonna (of interest because she is dark skinned, a woman, and also represents other things left out by the masculine light-seekers.)
Shadow work at collective and individual levels
So there is shadow work at both collective and individual levels: we notice the split, the (undesirable) consequences of the split, and try to mend it at social and personal levels - using whatever means are available to us.
Shadow work, in whatever forms it takes, cannot itself bring about a shift, but it can certainly set the stage for shifts and deepening to take place. Without it, there is little chance for any shift to occur.
And this includes, for those of us into those things, a shift into endarkenment - where the fertile and dark ground of form comes alive in immediate awareness.