While the sea is the source of earthly life, the symbolic sea of the collective unconsciousness (cu) is the source of our psychic life. In the sea of the cu are all the images–they are actual energies–that are common to all people on earth, both dead and alive, through the eons: the Great Mother, God the Father, The Child, The Wise Old Man, and, interestingly, the Tarot cards, to name a few. Jung works his archetypal theories around these images that reside in the cu. He spends a lot of time on the Mother archetype.
The cu appears to be a dark realm because it is outside our human consciousness. After all, our consciousness, our knowledge, is symbolized by light. We humans bring light to the world. However, consider the Hubbel H0liCOW project estimates the Universe is expanding at about 45 miles per second. Are we doing that with our minds?
We know for sure the collective unconscious exists when it wants to get our attention. It sometimes will give us psychological pain–the kind of pain you might run to the professionals for. This emotional pain, in psychoanalytic terms, are neuroses. We won’t go into all that here. Just know that Jung said consciousness is created by the emotions–no pain no gain.
The cu (some say God) wants to be known by you. The more fish (unconsconscious contents) you land on the shore of consciousness, the more “God” becomes manifest in our world. See? We can be intentional about it. The creation of consciousness–making conscious the unconscious–is a great work.