Why does it say "Katzafti"?
Radak: All this punishment is due to Yisrael. I was angry at them. They are My inheritance and portion from all the nations. When I was angry at them, I did not have mercy for you.
How did Hashem profane His inheritance?
Malbim: I removed their Kedushah and glory via "va'Etnam b'Yadech." Yisrael in the hand of Bavel is compared to a son who rebelled against his esteemed father. His father gave him to a base man to punish him, and gave power and authority to the base man so he would subjugate his son. The base man should have realized that (a) He should have mercy on him, for he is from an esteemed family; the punishment that he is under his hand suffices for him! Also refer to 47:7:3:2.
What is the significance of "Lo Samt Lahem Rachamim"?
Malbim: You did not put on them the special mercy proper for them, especially since they are My nation and inheritance.
Why does it say "Al Zaken Hichbadta Ulech"?
Rashi: You put a heavy yoke on the elders. They could not bear its weight.
Radak, Malbim: It is normal to honor elders and not burden them. Also Yirmeyah said "Pnei Zekenim Lo Nehdaru" (Eichah 5:12).
