kayena manasa buddhya
kevalair indriyair api
yoginah karma kurvanti
"The yogis, abandoning attachment, act with body, mind, intelligence and even with the senses, only for the purpose of purification."
Here Sri Krishna is setting up the the Customs of eldrs [aacharam] as an example we have to emulate. Earlier He told that just as water does not stick to a lotus leaf, papa of any Karma will not stick to that person who does Karma with the concept that the organs are doing their assigned duties, that karma is not done by atman[ me] and that not desiring for lower rewards. Now He cites that ancestors lived like that only. Kayena = by body, manasa = by mind, buddhya = by resolve, kevalair indriyair api= and even by the organs without 'I-am-doing' feeling, yogina = he who has practiced Karma yoga, karma kurvanti = is doing his activities, sangam tyaktva = relinquishing rewards, atma shuddhaye = but only for the purification of his mind. In every action we have to have the unity of mind, body and word or speech. That is one should speak what the mind thinks and act according to speech. Such persons are all called Mahatma. Karma yogi will act like this and will always be constantly thinking of atman. They do not desire any rewards because they want their mind to be removed of all pollutants and become pure.