Our Gemara on Amud Aleph discusses the legal technicalities of whether a rental or hire incurs financial obligation from commencement, or only at the end, when the rental or work contract is completed. Halachically this has implications for whether advance payment at a discount is considered charging interest or not. The halacha is that the obligation to pay a rental fee is incurred only at the end of the rental period. 

The Chida (Midbar Kdemos, Tav 10) uses this halacha to explain why we do not receive reward for mitzvos in this world, but then he adds an interesting twist. Since we are obliged to perform the mitzvos, our reward only comes upon completion of our contractual terms, which is the end of life. However, that only applies to obligations. Other aspects of mitzvah observance such as Hiddur Mitzvah (beautifying a mitzvah), and I would say, lifnim mishuras hadin (choosing to go beyond the strict letter of the law) are not included in the contract. Therefore, the Chida asserts, for such observances one can receive reward in this world as well. Aside from this being clever derush, it fits in well logically, based on what we discussed in the previous daf. Mitzvos bring a social and psychological benefit that is separate from the promised reward. Such benefits are surely activated when a person’s devotion extends to commitment that is beyond the letter of the law. It shows and creates an internalization of the ethics and attitudes within the law and so its benefit .