According to Boehme, cosmogony recapitulates theogony. That is, creation is preceded by, and echoes, the primordial “birth of God”. In a “beginning before the beginning”, there is only the primal Abyss or chasm of the Ungrund, containing the unoriginated divine Will. This Will generates a Son, and breathes forth its energies as a Holy Spirit. Of these three principles the first (unoriginated Will) is a principle of darkness or mysterious fire in the “Unground” of God’s mystery. The second (the Son) is a principle of light, corresponding to the Will’s apprehension of itself as truth. The third is a reconciling force, in which the previous two are united – the radiation of the fire in the light. Through this third principle, which describes the operation of the Holy Spirit, the fulness or content of the divine nature streams out into the void and (having, one supposes, nowhere to go) is “reflected back” from it as though in a mirror. To this illuminated reflection Boehme gives the name Sophia, Wisdom. At first no more than a dream of the divine Imagination, when clothed by the desire of God in an eternal, imperishable body she becomes “Uncreated Heaven”, the Kingdom of Beauty or Body of God in which his Glory is forever manifested.
Boehme supplies further detail concerning this "eternal construction" of Heaven, which is the model for all subsequent creation. The three divine operations (which we associate with the Ternary of Father, Son, and Spirit) establish a separation between darkness and light within the divine nature itself, whilst reconciling the two in an eternal harmony. As far as I can understand it, the dark or “Nature Will” consists of a dynamic tension of three archetypal forces or energies, which he calls Salt (contraction), Mercury (expansion) and Sulphur (rotation). This is the “Wheel of Life”. A fourth energy called the “Lightning Flash” marks the transition between darkness and light, or the point where divine Love overcomes the darkness of the wheel, transfiguring it into a Light or Spirit Will consisting, again, of three energies (making seven in all). Contraction becomes the vital fluid symbolically called “Water”, expansion becomes “Sound” (vibration or rhythmic motion), and rotation becomes the “Essence” integrating both, for which a better term might be “Music” – music being, as Bishop Martenson suggests in his commentary, the best earthly symbol for the Kingdom of God.
In language that is less alchemical and more theological, one might say that the Trinitarian Will of God has entered into the knowledge of itself by reconciling in Love the otherness of Father and Son. God eternally “becomes” what he eternally already is: a Trinity of Persons enthroned in an Uncreated Heaven full of peace and beauty.
Illustration from Wikipedia Commons: Boehme's Cosmogony, "The Philosophical Sphere or Wonder Eye of Eternity" (1620).