When perfection holds sway, there is certainly no need for service at all, for nothing could be better than His complete perfection. If so, fulfillment of the commandments would not add anything to it, or to His government of the world. But in a situation in which deficiencies exist, fulfillment of the commandments is of benefit, because through them, that which is imperfect and deficient is able to attain perfection. If so, only a realm of deficiency provides the appropriate arena for service in this way. Service is very applicable in a realm of deficiency. For it is impossible to speak of oneness and unity without speaking of absolute power and control without any limits. It follows that if He desires to actually reveal this unity, He will create a limitation and then remove it.
Why Performing Mitzvot Matters If God Is Already Perfect
Kalach Pitchei Chokhmah 4:7