The fifth skill of formulating a detailed plan of instruction takes place at the level of the sefirah of netzach ("victory") and of hod ("thanksgiving"). These two sefirot, which represent the two halves of the body (particularly the two legs), always appear as a pair. While the arms and hands can (and generally do) operate independently of each other, the legs cannot, for walking is necessarily a cooperative venture. For this reason, the metaphors for netzach and hod always depict two mutually dependent halves of a pair as in the two arms of the scale of justice.
Interestingly, the Hebrew word for "scales" (moznanim) has the same numerical value as netzach. Just as in a scale, when the balance tips, there is a winner and a loser, so in the relationship of netzach and hod. On the one side is victory, decision-making, ability to make correct, practical life decisions on the spot. On the other is thanksgiving, agreement, and the ability to concede to another's decision, surrender resistance, eliminate doubts and put full energy behind its actualization. This is the source of strength in the fulfillment of the decision.
The sefirot of netzach and hod also relate to the kidneys, which are called the "seat of practical advice." The ability to weigh information, diagnose the problem, and design a strategy of rectification requires analysis, but of a more pragmatic sort than that performed by the sefirah of binah ("understanding"). Analysis of practical life situations (obstacles and the way to overcome them) involves careful contemplation, much more so than that which takes place at the level of mind. Yet often the entire complexity of the matter must be instantaneously processed in reaction to an immediate event and a final decision delivered on the spot.
From the narrative of the Torah, we see that Moses was the decision-maker, the prophet, the transmitter of God's instruction, while Aaron was the peacemaker. It was Moses' task to relay the word of God exactly as he had received it. But it was Aaron's task to demonstrate that human words can be altered for the sake of peace. Together, Moses and Aaron brought into reality the vision of the Patriarchs who preceded them. They led the metamorphosis of the descendants of the twelve sons of Jacob from a collection of individuals into the nation of Israel. They led the redemption of the Jewish people from Egypt to their encounter with God at Mt. Sinai; they built the Tabernacle; they brought the nation to the boundaries of the Holy Land. Their roles were equally essential.
Moses is called "good" (tov) in the Book of Exodus: "she [his mother] saw him, that he was good." 'Good’ is the essential property of 'light' as we read in the Book of Genesis: "And God saw the light, that it was good." Based on this equation, the sages teach that when Moses was born, the whole house was filled with light. Another opinion suggests that the description of Moses as "good" means that he was born circumcised; he was born good in that no further rectification was necessary, there was no physical impurity to block the light of his soul. This is another way of connecting him with the role of decision-maker. To be born circumcised is also a metaphorical way of saying that his first and spontaneous impulse was always reliably good, correct and constructive. It did not need fixing or removal of impurities.
This is also the idea of "the good oil" referred to in the Book of Psalms–an oil that was used for anointing the head. The "good" is Moses; the "oil" is Aaron:
Behold how good (Moses) and how pleasant (Aaron) it is for brothers (Moses and Aaron) to dwell together in unity! It is like the good oil upon the head (Moses), running down the beard, the beard of Aaron
