|Chapter 3: Karma-yoga|
te deva bhavayantu vah
sreyah param avapsyatha
The demigods, being pleased by sacrifices, will also please you, and thus, by cooperation between men and demigods, prosperity will reign for all.
Srila Prabhupada explains, "The demigods are empowered administrators of material affairs. The supply of air, light, water and all other benedictions for maintaining the body and soul of every living entity are entrusted to the demigods, who are innumerable assistants in different parts of the body of the Supreme Personality of Godhead. Their pleasures and displeasures are dependent on the performance of yajnas by the human being. Some of the yajnas are meant to satisfy particular demigods; but even in so doing, Lord Visnu is worshiped in all yajnas as the chief beneficiary."
It is interesting to note that Krishna is apparently contradicting a statement He had earlier made in 2.46, where He recommends against following the rules and regulations of the Vedas (which is worship of the demigods) and focus on the real purpose of the Vedas (which is worship of Krishna, the Supreme Personality of Godhead). This contradiction can be explained by understanding that at this point Krishna is talking about a preliminary state of spiritual advancement, which if practiced sufficiently will elevate the person to develop faith in the cause of all the demigods, namely Lord Vishnu. Thus in 2.46 Krishna talks about a much higher state of spiritual realization than what He discusses here.
Please read the Sanskrit Verse and the Prabhupada's Purport.