The Sefirot are what Eyn Sof wanted to reveal of His attributes.
Each Sefirah is one of His attributes (middot) — Kindness, Judgment, Mercy, and so on — never one of His Essences.
Op. 5 told you what kind of thing a Sefirah is: a visible light. Op. 6 tells you what each Sefirah is in content. Klach's answer is that each Sefirah is one of His attributes — Chesed (Kindness), Gevurah (Judgment), Tiferet (Beauty/Mercy), and seven more — by which He created and continues to govern the worlds. The chapter completes the structural definition of the Sefirot the book will rely on for the next 132 chapters.
When we speak of a person's attributes, we mean the qualities they exhibit in their actions: someone is kind, generous, patient, just. The qualities are real features of the person, but they are not the same as the person. Kind is something he is in his actions; the person himself is something else, something that has kindness among other qualities and could in principle act differently if he chose.
The Sefirot stand to Eyn Sof in something like this relation. Each Sefirah names one of the ways His Will operates — one of the middot, the operational qualities — by which the cosmos comes into being and is governed. Chesed is the way He gives without limit; Gevurah is the way He limits and judges; Tiferet is the way He reconciles the two; Netzach, Hod, Yesod, Malchut name further dimensions of how His Will reaches the world. These are real features of His operation, not poetic decoration. But they are not features of His Essence; they are features of His Will, and the Will / Essence restriction of Op. 1 still holds.
The most consequential phrase in the chapter is what He wanted to reveal. The Sefirot are not all of His attributes; they are the attributes He chose to make visible. If He had wanted to operate through different attributes, He could have. The configuration of the Sefirot is not metaphysical necessity. It is the configuration He selected for the cosmic plan He set up — the calibration that, as the next section will explain (Op. 14), is exactly what was needed to produce free-willed creatures who can earn the bestowal.
This settles a question that often confuses first-time readers of Kabbalah. When the tradition speaks of God in terms of Chesed, Gevurah, Tiferet and the rest — and the language can feel concrete and almost personifying — it is not naming what God is. It is naming what He has chosen to reveal of His Will. The strict restriction of Op. 1 is preserved here completely. The richness of the language is the richness of what He has shown us, not a description of what He is in Himself.
Op. 6 also makes a structural claim that the rest of the book will quietly use throughout. The Sefirot are not separate from Eyn Sof; they are the parts of Him that He reveals. When the book later treats the Partzufim, the breaking and repair of the vessels, the operational coupling — every one of these technical structures will sit on the doctrine that they are His Will revealed in operation, never independent realities.
The attribute-doctrine returns at Op. 14, where the Highest Thought is shown to have calibrated exactly these attributes for the goal of producing free will. It returns again at Op. 17, where the distinction between Sefirah (the underlying attribute, the Cordoverian focus) and Partzuf (the same attribute fully articulated as a Likeness of Man, the Lurianic focus) is drawn. And it grounds Op. 25's cosmogonic claim that the Sefirot are Godliness in essence (bound up with Eyn Sof) but visible by His Will — never independent things.