What is the meaning of "Al Ken Chatzavti ba'Nevi'im"?
Rashi: Because I engraved My words via the Nevi'im? (refer to 6:5:2:1. "Al Ken" is like Al Asher. The same applies to "Ki Al Ken Ra'isi Fanecha", "Ki Al Ken Lo Nesatiha l'Shelah Veni" (Bereishis 33:10, 38:26).
Radak: This is like Chotzev (quarrying) in a mountain ? he cuts the rocks.
Radak citing Targum Yonasan: Because I warned them [via My Nevi'im, and they did not repent, I killed them].
How did He kill them "b'Imrei Fi"?
Rashi citing Targum Yonasan: I killed them due to My words, because they were not careful with them.
Radak: Because your Chesed is like a morning cloud, I wearied the Nevi'im every day early, to warn you to go on the straight path; you did not listen. I wearied them so much, it is as if I killed them.
Radak citing his father: They died via My Shelichus, e.g. Zecharyah and Uriyah.
Malbim: [I killed them because] I desire Chesed, and not Korbanos. The Nevi'im told them so; He desires only Chesed and that they know Da'as Elokim. The nation killed the Nevi'im due to this Nevu'ah. The verse depicts that Hashem killed them. Since they gave their lives for this, it remained in the heart of future generations, like something engraved with an iron stylus into rock, for a permanent remembrance. The verse depicts that the bodies of the murdered Nevi'im were like stone tablets on which Hashem carved these words "Chesed Chafatzti v'Lo Zavach" (6).
Why does it say "u'Mishpatecha Ohr Yetzei"?
Rashi: This is said in astonishment. How can I show favoritism to you due to Midas ha'Din? This refers to above "Mah E'eseh Lecha" (4).
Radak: All this was in order that your Mishpat will be like light that goes out, i.e. when it goes out.
Malbim: This is a Ma'amar Musgar (parenthetical comment). Hashem sent His Nevi'im to rebuke the nation, who thought that via their many Zevachim (Shelamim) and Olos, they bribe Hashem, and this will atone, to the point that they are permitted to do evil ? "ha'Ganov Ratzo'ach v'Na'ef v'Hishave'a la'Sheker?; u'Vasem va'Amadtem Lefanai ba'Bayis ha'Zeh Asher Nikra Shmi Alav va'Amartem Nitzalenu" (Yirmeyah 7:9-10). If your sword consumes Nevi'im like a vicious lion, how will you be vindicated in your judgment?