Why does it say "Sab'enu va'Boker Chasdecha"?
Rashi: [Satiate us with] the day of redemption and salvation, which is morning to the night of affliction, sighing and darkness.
Malbim: Do one of two things. (a) Immediately in the morning (the beginning of life - youth) You will satiate us with Your Chesed, and we will not see evil occurrences, so we will rejoice in all our days. Also refer to 90:15:1:5.
Why does it say "b'Chol Yameinu"?
Rashi: [After the salvation, we will rejoice] over all the afflictions that came on us in these days.
Ibn Ezra: If we will be satiated with Your Chesed in the morning - You will teach to us the straight path in our youth 1 - we will rejoice the entire day, i.e. all our days, even in old age.
Radak: There will not be more afflictions.
Ohr Yisrael 30, Mishnas R. Aharon 4 p.14: Chesed is Torah - "Chesed Kel Kol ha'Yom" (52:3). The primary Avodah is in one's youth - the Midos are soft, and one can straighten them. Afterwards, the Midos are fixed.
