I am the doer, I am the  deeds of Yagya (projects), I am the offerings (the investments into the  projects) and I am the medicine (solution to the problems). I'm the Mantra  (principles in the chants); I am the fuel (butter-ghee that sustains the fire, in  other words the motivation that binds people till success), I am the fire (the  activation and propulsion of deeds, the sequence of actions during Project); I  am the oblations (the contribution of people in many ways). 
  Any activity, event and project is said to be Yagya.  These great actions or Yagyas are performed by the people through different  means and modes directed by Prakriti and Purusha. In this Shloke too Lord  Kritsna represents Brahm and takes the ownership of deeds and their cause. This  is similar to Shloke 3.15 and 4.24 where the Lord says that actions are by the  Brahm, for the Brahm, fuelled by Brahm and executed by Brahm.
  Superior to  materialistic yagya is the Yagya of knowledge, O' Parantapa (name of Arjun).  All actions in the universe finally culminate into the knowledge.
Best of Yagya is knowledge as said in the Shloke.  Unfortunately most think that Religions and science confront each other. As per  Santan Dharma they should love each other the most.
  By projects of knowledge  (high efforts and deeds in research of truth) and via other projects (Yagya) of  utilitarian good too, some worship Me. One is He or distinct, He is reflected  in many ways in world.
God reflects itself in many ways in this world.  Different people conceptualize Gods differently and pray. People worship Gods  in yagya many ways, such as by belief by utilitarian action by knowledge by  research etc. True Yagya starts after prayer around the altar  of fire. Demonstrative parts of prayers are only a team-building  exercise, real worship lies in enacting God's ways. When scientists research  and discover new findings, they actually worship Gods by studying His laws.  Brahm is demonstrated in various phenomenon of nature. One may worship Him as  one or many. Sanatan Dharma provides such flexibility to conceive God as one or  many forms or even formless. Thus, the root of all the world's religion are  from Sanatan Dharma. Such a secularity is unique to Sanatan Dharma.