The process is not a punishment or about punishing the body. It is about self-improvement and development. The key is to remain engaged and committed. A disciplined lifestyle makes our participation meaningful.
Sometimes we are given a small taste/experience of heaven (darshan) from time to time to keep us motivated. This small taste attracts our attention. The more attention we pay, the more we become engaged. A disciplined lifestyle keeps us locked into that golden space for longer and we receive many benefits. These may be physical and spiritual benefits but include others such as preparation for the next stage/class.
As the process is long some benefits are not immediate. To remain disciplined, we create the hunger for more and we establish a strong reason or purpose. The mann only works on purpose and interest. The higher the purpose, the stronger the motivation. The strongest purpose is salvation (mukti).