Why does it say "va'Yizkor Ki Basar Hemah"?
Rashi (38): [He aroused only a little anger] because He remembered that they are flesh, and the Yetzer ha'Ra is hidden in their hearts.
Radak: The nature of flesh is to seek desires; it is impossible that it will not sin. Therefore, he needs to atone for them.
Malbim: Flesh is prone to sin based on its nature and its Yetzer ha'Ra.
Why does it say "Ru'ach Holech v'Lo Yashuv"?
Rashi (38): [The Yetzer ha'Ra] is Ru'ach that goes when they die, and it never returns to them. When they will live in the world to come, the Yetzer ha'Ra will not rule over them 1 .
Radak: Their days are short and they need Kaparah while they are still alive - "u'Meh Lo Sisa Fish'i v'Sa'avor Es Avoni Ki Atah le'Afar Ashkav" (Iyov 7:21). Based on nature, once the Ru'ach leaves, "v'Lo Yashuv"; it is a wonder that Hashem will return it to the flesh when He wants; it will not be for everyone. It will be a wonder like a supernatural miracle.
Malbim: The inner Ru'ach is the power that puts images on the heart, which arouses sin. The Ru'ach dies with the flesh; it is like flesh, which is prone to every sin.
Rashi (from Shocher Tov): You cannot explain that Ru'ach of life will not return to them. If so, you deny Techiyas ha'Mesim!
