1)
Who are the witnesses, and what do they testify about?
1.
Rashi: They testify about the changing illnesses and pains.
2.
Ibn Ezra: The plagues [on my body] testify. Malbim - they testify that I sinned and deserve to be punished. .
2)
What do we learn from "Chalifos v'Tzava Imi"?
1.
Rashi: There are fixed times for my afflictions. These serve and switch with others that serve at another time.
2.
Ibn Ezra: They go and stay. This is like "ha'Lo Tzava" (7:1).
3.
Malbim: I am under Tzava and time. It looks like my deeds change via my choice, so You get new witnesses. Really, Your knowledge is a chain that suppresses my power; I have no choice. I should not be punished!
