The rule of good and evil and the rule of unity.
The Tzimtzum embeds both the rule of good-and-evil (operative now) and the rule of unity (operative at the cycle's end), from the outset. The Other Side stands parallel to the Holy Side under one government.
Op. 30 is the doctrinal hinge of the Tzimtzum unit and one of Klach's most consequential chapters. The Tzimtzum, as Op. 24 defined it, was a willful self-restriction. Op. 30 reveals that this single act embedded two cosmic-temporal rules from the outset. Both rules are real; both are operational; their simultaneity defines the cosmic plan.
The rule of good-and-evil is operative now. In the cycle's middle phase, the cosmos contains both Holy Side and Other Side — two parallel structures, one good and one evil, each operating with its own internal logic. The Other Side is real but bounded; created, not eternal; innovated in the act of Tzimtzum, not part of Eyn Sof's prior reality. God made also this one against this one (Ecclesiastes 7:14) is the chapter's structural anchor.
The rule of unity is operative at the end. When the cycle completes, the rule of good-and-evil dissolves. The Other Side reverts to good (the doctrine of Op. 49); only the rule of unity remains. The Tikkuney Zohar passage Klach cites is striking: when the Four-Letter Name rises from the Throne of Judgment and Throne of Compassion, there will be no punishment or reward. The cosmic-temporal architecture has both phases built in.
Three differences between Holy Side and Other Side are crucial. First: the Holy Side is Eyn Sof's Will operating; the Other Side is a created realm that operates within His Will's framework. Second: the Sefirot are calibrated (exactly required for the cosmic plan); the Other Side is bounded (limited, finite, never sovereign). Third: the Holy root is primordial (it has always been intended); the Other Side is an innovation (it was set up by the Tzimtzum, for the cycle's middle phase, with a structural endpoint).
The chapter also introduces the Kav HaMiddah — the Line of Measurement, boutzina d'kardunita — the cosmic power that institutes boundaries through successive concealments. The same boundary-making power that produces the operational structures of the cosmos also produces the conditions under which the Other Side can exist.
The two-rules doctrine is the structural foundation of every later treatment of evil and repair. Op. 43–45 (the Other Side's location and structural basis); Op. 47 (the level-by-level repair); Op. 49 (the cosmic arc — production of evil, return to good); Op. 138 (the operational asymmetry of present Couplings). Every one of these chapters operates inside the Op. 30 framework. The cycle's end — complete repair for ever to eternity (Op. 137) — is the moment the rule of unity displaces the rule of good-and-evil.