The result of the Tzimtzum: the Sefirot became visible.
The Tzimtzum's productive result is visibility: it removes the limitlessness that would have made the Sefirot invisible. The Sefirot are Godliness in essence, but their visibility is willful.
Op. 24 told you what the Tzimtzum is. Op. 25 tells you what it does. The Tzimtzum's productive consequence — the reason the contraction is part of the bestowal-plan — is that it makes the Sefirot apprehensible. Without the contraction, the Sefirot could exist only as implicit aspects of Eyn Sof's unseeable Will; with it, they become visible attributes.
This sharpens the permitted to be seen qualifier of Op. 5. There, the Sefirot were introduced as visible by His permission. Op. 25 explains the cosmogonic cost of the permission. He had to contract — willfully remove the encompassing limitlessness in one place — for the Sefirot to be seeable.
The chapter's sharpest move is in its preserved tension. The Sefirot are Godliness in essence. They are not separate things from Eyn Sof; they are bound up with Him. But their visibility is willful, not intrinsic. What we see when we see them is the radiance of His splendor — not His intrinsic essence. The Will/Essence restriction of Op. 1 holds completely. We see what He has chosen to make visible, never what He is in Himself.
This matters operationally for the rest of the book. When Klach later treats the Sefirot's anatomy, the Partzufim's structure, the coupling-mechanism of cosmic governance — every one of these operational claims sits on the Op. 25 framework. The structures are Godliness operating; their visibility is by the Tzimtzum's willful concealment-and-revelation.
Op. 26 will populate the contracted space with the Reshimu (the residue of the original simple light). Op. 27 will introduce the Kav (line) — Eyn Sof's perfect action entering the contracted space. The radiance of splendor terminology of Op. 25 generalises into the Op. 89 Dew of Bedolach doctrine — what descends from the upper concealment is radiance, never essence.