By the sixteenth century Kabbalah had three hundred years of accumulated material behind it, in the Zohar and in competing schools that used the same vocabulary to mean different things, and no orderly account of any of it. Cordovero, working at Safed, wrote one. The Orchard of Pomegranates, finished when he was twenty seven, takes the whole inheritance apart and reassembles it topic by topic, stating the positions, weighing them, and deciding.
The hardest question he took on is what the sefirot actually are. If the ten emanations are God, then God has parts and changes, which the philosophers had spent centuries denying. If they are not God, then Kabbalists are directing worship at something created, which is worse. Cordovero's answer is that they are vessels, and the divine light is what fills them: the vessel is not the light and the light is not the vessel, and yet what is in them is genuinely God, so that a person contemplating the sefirot is neither addressing an intermediary nor dividing the indivisible. He put it in a formula that later writers quoted constantly, that God is all reality but not all reality is God.
The book made Kabbalah teachable. It is the reason the Safed circle could train students rather than only initiates, and it is the systematic reference against which everything that came afterwards, including the system that displaced it, was measured.