His desire to bestow good to perfection through the revelation of His oneness is the cause of the deficiencies in the world, which create the conditions for man's service. The revelation of His oneness is itself the reward.
The plan: He conceals His perfection so that a realm of deficiency exists; in that realm, creatures serve through their commandments; the service reveals His oneness; the revelation of oneness is the reward.
The four stages, in order. First, He conceals His perfection. He does not give it up — that would not be possible — but He restricts its full visibility in one specific way, so that a domain becomes possible in which something other than His perfection seems to be operating. This is the act later named the Tzimtzum (which means "contraction" or "self-restriction"). It does not change Him; it changes what creatures can see of Him.
Second, the act of concealment produces a realm of deficiency. Where His perfection is fully visible, nothing more is needed. Where it is concealed, things appear to be incomplete, broken, in need of correction. The realm of deficiency is not a flaw; it is the necessary stage on which the cosmic plan operates. Without it, no creature could be in a position to serve, because there would be nothing wanting and no work to do.
Third, in the realm of deficiency, creatures serve. They observe the commandments; they choose good over the easier evil; they cooperate with the cosmic structure; they do the daily work that, accumulated across history, restores what concealment has hidden. Service is the operational role of creatures in the cosmic plan. It is what makes them deserving in the sense Op. 3 required.
Fourth, the service produces the revelation of His oneness. The same oneness that was the axiom of Op. 1 — declared at the start of the book — is what gets revealed at the end of the cycle. The revelation is not new content; it is the manifestation of what was true all along. And here is the most striking move in the chapter: the revelation of oneness is itself the reward. The bestowal of the ultimate good in Op. 3 turns out to be, in its fullest form, the unmediated experience of what Op. 1 said axiomatically. The cycle's beginning and the cycle's end are the same fact, viewed from different sides of the deficiency.
Op. 4 closes by citing back to Op. 1. The same oneness that was axiom is what is revealed. The arc of the entire book — the long working-out of cosmic structures, broken vessels, repaired Partzufim, coupling and pregnancy and birth — is, in one sense, the slow pedagogical extension of the four stages compressed into Op. 4.
The Tzimtzum forecast in Op. 4 is given its full cosmogonic definition at Op. 24 (localised, willful, path of limited action). The four stages of the plan recur structurally throughout the book; you will see the deficiency stage analysed across the World of Nekudim (Op. 36–50), the service stage in the discussion of human deeds across Op. 48 and Op. 137–138, and the revelation stage in the closing chapters' Coupling-order doctrine (Op. 138). The most concentrated return of Op. 4's revealed oneness claim is at Op. 16, where the cycle is named explicitly from Eyn Sof to Eyn Sof.