Why does it say "Zeh Ra b'Chol
Ibn Ezra, Metzudas David: This is the worst matter under the sun.
Ri Kara: This evil, that the same occurs to everyone.
What is "Asher Na'asah Tachas ha'Shamesh [Ki Mikreh Echad la'Kol]"?
Rav Sadya Gaon: It is everything created under the sun.
Seforno: One who strives to attain eternal life in investigation and deed, he needs also to strive to attain needs of temporary life, just like a commoner who strives only for temporary life. Many did like R. Shimon ben Yochai (engaged only in Torah, and not at all in income), and did not succeed in either (Brachos 35b).
Why does it say "v'Gam Lev Bnei ha'Adam Malei Ra"?
Rav Sadya Gaon: People's hearts are full of evil and depression in their lifetimes, because Mikreh Echad for all - their end is to die.
Rashi: People say that there is no judgment of punishment for Resha'im. Everything is chance - sometimes [afflictions] come to Tzadikim, and sometimes to Resha'im.
Ibn Ezra: It says Bnei ha'Adam 1 , for it is harsher for youths, due to their small Da'as.
Rashbam: Their hearts are full of evil, to do many evil deeds. They say, there is no loss via this, since the same occurs to everyone - all die. Resha'im persist in evil, and do not repent. This is wondrous - why does Midas ha'Din delay so much, and why does the same occur to everyone?!
Ri Kara: Since people see that a Tzadik's virtue does not help him, and a Rasha's evil does not make him stumble, their hearts are full of evil. If Resha'im would see a Rasha perish in his evil, and it is good for a Tzadik in his virtue, they would repent and do Mishpat and Tzedakah!
Seforno: One who strives in Torah and good deeds, he needs to neglect them to attain needs of temporary life. Another bad result of this is that people's hearts are full of evil. They think that man's intellect is merely in order to attain [needs of] temporary life.
Metzudas David: People say that there is no supervision, and no judgment.
I.e. children. (PF)
What is "Holelus bi'Lvavam"?
Rid: They think folly, like the verse will explain.
Metzudas David: It is befuddlement and confused Da'as.
What do we learn from "v'Acharav El ha'Mesim"?
Rashi: In the end, they descend to Gehinom.
Ibn Ezra: Their hearts [are full of evil in their lifetimes, and] after death, like the coming verses say.
Rashbam: After death, they cannot repent.
Ri Kara: Also this causes people's hearts to be full of evil. In their lifetimes, they consider that their end is to die, and then their Bitachon is lost, like the coming verse explains.
Rid: They think that in the end, everyone will join to the dead, and his straightness and virtue did not help him at all.
Seforno: People also have a bad mindset to think that a person's intellect perishes. Refer to 9:4:1:8.
Metzudas David: Their befuddlement does not depart until they die and go to the grave with the dead.