Boehme's difficulty is not obscurity for its own sake; he is trying to say something that his available vocabulary was not built for. He begins before God as usually conceived, with what he calls the Ungrund, the groundless: an unfathomable will that is not yet anything in particular, because there is nothing outside it by which it could be distinguished. Such a will cannot know itself, since knowledge requires something to stand against.
Everything else follows from that requirement. In order to become manifest, the groundless must generate a contrary within itself, a principle of contraction, desire and wrath, against which a principle of light and love can be revealed. Boehme is explicit that the dark principle is inside God and is not a mistake, and that without it there would be no manifestation, no nature and no world. Evil, in his account, is that principle detached and running on its own account rather than a substance created by anyone.
This solved a problem and created a worse one, and his critics said so immediately: a God with wrath in his ground looks like a God who is the author of evil. The influence was nonetheless immense and ran in directions he could not have anticipated. Pietism took him up, English readers formed a following, Newton's circle read him, and through Oetinger he reached German Idealism, so that Schelling's treatment of freedom and Hegel's account of a spirit that must go out of itself both have a shoemaker from Gorlitz somewhere behind them. Blake and the Romantics took the imagery, and Western esotericism has never let go of him.