246. The thirteenth Mitzva is to perform the redemption of a first-born son so as to strengthen him in life. For there are two appointed angels in charge – one over life and one over death. And they both rule over man from Above. And when man redeems his son, he redeems him from the angel in charge of death, so that the angel can no longer govern the first-born son. Hence, it is written, AND THE CREATOR SAW EVERYTHING THAT HE HAD MADE – this is in general, AND, BEHOLD, IT WAS… VERY GOOD alludes to the angel of life, while the word VERY alludes to the angel of death. Therefore, by this act of redemption, the angel of life is strengthened and the angel of death is weakened. Life is purchased by this redemption, for the evil side leaves him be and clings to him no more.
The ascent of the worlds occurred on the sixth day of creation: ZA ascended to the place of AA, Malchut ascended to AVI, and Adam attained Ohr Haya. As a result, the angel of death (egoism) lost his power completely. On the contrary, he became very good, for upon being corrected, egoism becomes a great and holy Kli, the one Kli that can receive the greatest Light.
Such a state will come at the end of the general correction, when, due to the revelation of this great Light, death (egoism) will disappear forever. This is the meaning of the verse: “when the Creator saw EVERYTHING that He had made (i.e., at the end of all creation), He saw that it was very good.”
However, since Adam's sin, the worlds can no longer ascend as high. This is why we need special Mitzvot in order to perform special preparations and actions for the reception of Ohr Haya, at least in a state called Shabbat. This is precisely the Mitzva to redeem one’s first-born son, when we weaken the powers of the angel of death and strengthen the angel of life, much like what the Creator did to Adam by the preliminary ascents of all the worlds, for during such an ascent, called Shabbat, the angel of death becomes very good. Such is the power of that Mitzva.
Yet, it is not observed as fully as previously, when the angel of death lost all of his power. Now, by observing the Mitzva of redemption of the first-born son, we merely distance from the angel of death without actually destroying the impure forces, and they no longer cling to him. And after preventing the impure forces from clinging, accomplished with the help of this Mitzva, he can receive life, i.e., Ohr Haya of the state of Shabbat.