What is the rhetorical effect of “fī” in “fī l-qiṣāṣi ḥayāh”?

Musāwāt and Ījāz al-Qaṣr: Proportionate Wording and the Rhetoric of Qiṣāṣ

• It equates all killings with lawful retribution
• It functions as an oath particle
• It links the institution of qiṣāṣ with the preservation of life
• It puts the subject in the accusative