Initially, the first partzuf of Adam Kadmon emerged, because immediately after the first constriction (tzimtzum), in which the fourth level was restricted from serving as a receiving vessel for the supernal light, and a partition was placed upon the fourth level, as stated above, the supernal light was drawn down to be enclothed in the vessel of Malkhut in its normal manner, that is, with the supernal light trying to fill any available space.
But the partition that formed on the vessel of Malkhut prevented this and rebuffed the light. By means of this impact against the partition of the fourth level, the returning light was elevated to the height of Keter of the ten sefirot of the supernal light. That returning light became the garment for the ten sefirot of the supernal light and the roots of the vessels for the ten sefirot of the supernal light, which are called the ten sefirot of the head in the first partzuf of Adam Kadmon.
Subsequently, that Malkhut expanded itself and spread together with the returning light, driven by the power of the ten sefirot of the head, to form ten new complete sefirot from above to below,39“Above to below” refers to the direction of the expansion of the returning light vessel of Malkhut as it now expands “downward” to form complete vessels. By contrast, when discussing the returning light that emerges from the partition, the description is “below to above,” because the flow of returning light moving to enclothe the supernal light is, in that context, rising from the partition upward. and thus the vessels were completed, having formed the level of the body.
Each shiur koma (literally, “dimension of height”) that emerged in the ten sefirot of the head was also enclothed in the ten sefirot of the body. Thus the first partzuf of Adam Kadmon was completed, containing both levels of head and body.