What is "Tefachos"?
Rashi: Man's days are measured and fixed, like something measured in Tefachim (handbreadths). Malbim - this shows that I am from the physical, limited world.
Radak: Tefach is the smallest Midah 1 . So are my days; man's life is short.
Etzba is smaller! Perhaps he means the smallest measure used for Mitzvos, e.g. Shabbos, Lulav, Sukah
What is "Cheldi"?
Rashi: It is my old age. It is an expression of Chaludah (rust).
Radak: My time.
Why did he say "v'Cheldi ch'Ayin Negdecha"?
Malbim: My intellect sees itself as being unlimited. However, physicality (being tied to the body) weighs down the Nefesh and limits it. It is Batel to Hashem.
What is the meaning of "Kol Hevel Kol Adam Nitzav"?
Rashi: Every living person, his life and situation are folly.
Radak: This that man stands in this world, it is folly. Kol Hevel is the smallest Hevel, like "Hevel Havalim" (Koheles 1:2). Kol Adam is any man, like "Kol Melachah Lo Sa'asu", "Kol Chelev v'Chol Dam" (Vayikra 23:3, 3:17).
Malbim: Man is Hevel regarding the body, which wears out and decays, and also regarding the Nefesh, which is fettered (cannot reach to Shamayim, like it wants).
Why does it say "Selah"?
Malbim: This concludes this part; afterwards is the answer.
