Why does it say "Harbe ha'Etzim"?
Malbim: I will strive to increase the wood and kindle the fire inside, until the meat will finish.
What is the meaning of "Hasem ha'Basar v'Harkach ha'Merkachah"?
Rashi: When the meat ceases from on the bones, and it shrivels and mixes with the gravy, and he stirs with a spoon, it is like a blend of spices.
Radak: When the meat is cooked, they put in the pot spices to make it tasty; this is called Rekach Merkachas. The Mashal is, they will be finished in the city amidst great Tzaros, and are ready for the sword to consume them, just like meat is ready to eat after it is cooked and spiced. The bones are a Mashal for the Gedolim, like I explained (5).
Malbim: The meat will cook until it loses the form of meat. It will be like a Merkachah, and something fine combined with the heat of fire, until also the bones will burn. The water will be finished, and everything will burn, including the bones in the pot.
What do we learn from "veha'Atzamos Yecharu"?
Rashi: Amidst shriveling of the meat, the bones burn, dry and smoke. This is like "Charah Mini Chorev" (Iyov 30:30). Radak - Yecharu is Nif'al conjugation from the root Charar, like "v'Shachan Chararim ba'Midbar" (Yirmeyah 17:6). It is a place that is burned amidst great heat.
Malbim: Refer to 24:10:2:3.