Final answer:
The sentence 'an eye for an eye' is most closely associated with the sentencing goal of retribution, which focuses on imposing punishment that is proportionate to the crime committed.
Step-by-step explanation:
The sentencing goal closely associated with the phrase 'an eye for an eye' is retribution. Retribution aims to provide a punishment that is proportionate to the crime committed, mirroring the historical context of the phrase which sought to limit retaliation to be no more severe than the original harm caused.
In contrast to other sentencing goals like rehabilitation, which focuses on transforming the offender into a law-abiding member of society, or deterrence, which aims to discourage crime, retribution is primarily about enacting justice by punishing the offender.