Text 13 

pancaitani maha-baho
karanani nibodha me
sankhye kritante proktani
siddhaye sarva-karmanam 

Translation

O mighty-armed Arjuna, according to the Vedanta there are five causes for the accomplishment of all action. Now learn of these from Me. 

Commentary by Srila Prabhupada 

A question may be raised that since any activity performed must have some reaction, how is it that the person in Krishna consciousness does not suffer or enjoy the reactions of work? The Lord is citing Vedanta philosophy to show how this is possible. He says that there are five causes for all activities, and for success in all activity one should consider these five causes. Sankhya means the stalk of knowledge, and Vedanta is the final stalk of knowledge accepted by all leading acaryas. Even Shankara accepts Vedanta-sutra as such. Therefore such authority should be consulted.

The ultimate control is invested in the Supersoul. As it is stated in the Bhagavad-gita, sarvasya caham hridi sannivistah. He is engaging everyone in certain activities by reminding him of his past actions. And Krishna conscious acts done under His direction from within yield no reaction, either in this life or in the life after death.

Commentary by Sri Visvanatha Cakravarti Thakur

"But how can doing action not give karmic results?"

In order to establish that there is no contamination of karma when performing actions without false identification, the Lord speaks five verses.

For the completion (siddhaye) of all actions, know these five factors from my words (me). Sankhya means to speak (khya) directly (samyak) about the paramatma. These five causes are mentioned in the Vedanta scriptures (sankhye), whose purpose is to destroy karma (krtante).