annad bhavanti bhutani parjanyad anna-sambhavah yajnad bhavati parjanyo yajnah karma-samudbhavah
Translation
All living bodies subsist on food grains, which are produced from rains. Rains are produced by performance of yajna [sacrifice], and yajna is born of prescribed duties.
Purport
In this Shloka, Bhagvan Shri Krishna explains the material cycle of Yajna. As explained in Sh#11,12, deities are the higher beings who nurtures human of the physical needs. Human please deities by performing Yajna and deities fulfill the desires of humans. This shloka also explains why a big part of Veda Samhita is nothing but the hymns of performing Yajna to please deities.
