Mugeuk is a state in which yin and yang are present but not manifested. The seed is there, the soil is there, but there is no visible change yet.
This change begins to occur when water, the energy of life, is supplied and the yin and yang become clear. This process of transformation as yin and yang becoming clearer is called Taegeuk.
At the end of this process of transformation, a sprout emerges from the ground and grows, which we call the Hwanggeuk.
Everything in the universe reveals itself through this process.
So does the process of enlightenment. Everyone has the seed of God in their head, but it is in a state where nothing has happened yet.
When one's mind is correct, the qi follows it, so the water qi rises upward and the fire qi descends downward. By that, the head begins to be supplied with water qi, which is the energy of life, the pineal gland is activated, yin and yang become clear, and change begins to take place in the spirit and soul.
That means, if you continue to cultivate your mind, you will reach a state where your spirit and soul become one with heaven and earth, which we call union of God and Human. When you reach this state, you have attained full enlightenment.
Phoenix