Why does it say "v'Shamatetah"?
Rashi: Bal Korchecha (against your will) your land will cease [to be farmed] for [the same number of year] it did not rest in your [agricultural] Sabbaths (Shemitah year). I told you "v'Shavsah ha'Aretz" (Vayikra 25:2)!
Radak citing Targum Yonasan: A hater will come on your land and it will be desolate like in Shemitah.
Malbim: There are two Perushim. (a) You will cease from your inheritance. After Gedalyah died, [the remaining Jews] went to Egypt and abandoned the land. Had they remained in Eretz Yisrael, it would not have been desolate, for [Nevuzaradan] left Jews to be Chormim and Yogvim 1 . (b) Via this, there was Shemitah also among the Jews. They went from freedom to slavery; they served their enemies in Egypt, for Nebuchadnetzar conquered all of Egypt afterwards.
These are people who tend vineyards and work in fields, respectively. (Radak Melachim II, 25:12 citing Targum Yonasan).
Why does it say "u'Vecha mi'Nachalasecha"?
Rashi #1: I will take vengeance against you due to your inheritance that I gave to you. You did not do My will to cease [working] it.
Rashi #2: I will take vengeance against you from your inheritance; I will exile you from it.
What is the meaning of "Ki Esh Kedachtem b'Api"?
Rashi: You ignited fire in My nostrils.
