Why did he say "Lamah Ira"?
Rashi (5): Why do I fear [on the day of payment for sins]?
Radak: Why should I worry about wealth and acquisitions? They are honor of this world. If I will worry about good of this world
What are "Yemei Ra"?
Rashi (5): They are the days of payment for sins.
Radak: They are the days of this world. They are evil to all who engage with them.
What is "Avon Akevai"?
Rashi (5 from Tanchuma Ekev 1): They are sins that I trample with the heel. I belittle them, because they are light in my eyes; they convict me, and all the more so the rich [should fear].
Radak #1: [If I will seek good of this world,] I will encounter sin at the end of my deeds. I.e. if I am happy at the beginning, at the end I will worry. Since the heel is the end of man, the end of every matter is called Ekev.
Radak #2: Akevai (my end) is the world to come, i.e. the world of reward and punishment. They are at the end of the deed. I.e. even if I am happy with the good of this world all my days until death, I will not rejoice in the world to come after death. It is Akevai, the end of deed - "Ein Ma'aseh v'Cheshbon" (Koheles 9:10) in the world to come. There will be punishment for my deeds, for rejoicing in the good of this world and pursuing it. Therefore, I should not go in the path of those who trust in their wealth.
Malbim: They are the sins that I went and conducted in them, and I did not guard to prepare for myself provisions for the destined day [of death], and do something to perfect my Nefesh.
