﴿فِي الْقِصَاصِ﴾
In qiṣāṣ, that is, within the institution of just retribution.
The preposition fī literally suggests containment and here forms a close relation between the legal measure and the life it helps preserve. What might look outwardly like a contradiction becomes an insight into deterrence and collective protection.
The definite al-qiṣāṣ identifies an established legal institution, not uncontrolled personal revenge. This distinction is crucial for understanding the reasoning.