“O you who believe, prescribed for you is legal retaliation” (Qur'an 2:178).
The law of retaliation addresses believers while dealing with the grave wrongdoing of unlawful killing. The theological point is not that murder is light, but that legal punishment for an offense and the judgment of unbelief are distinct questions. A scriptural discussion of an offense may remain within the general address to believers.
The verse must still be read in its wider context, and the legal conditions for retaliation require separate juristic analysis.