Thank you for the opportunity to help you with your question!
The philosophy of sentencing, in general, relates time sentenced to crime severity. The more severe a crime is, the more time served.
This philosophy falls prey to changing values, incorrect or faulty assumptions about what will deter people from crime, and the very difficult task of deciding crime severity.
Rehabilitation is used as an alternative to sentencing with the idea that many crimes are committed for reasons that can be solved with therapy. This is meant to stop repeat behavior and avoid the typical drawback of sentencing, which is the high rate of recidivism.
Please let me know if you need any clarification. I'm always happy to answer your questions.