The 13th, 14th and 15th verses discuss the five factors involved in any kind of activity.

14th verse: “In any activity, there are five factors involved. (1) adhiṣhṭhānam – The body-mind-complex, which is the basis of all actions. (2) kartā – the agent of action, which is the jivatma. (3) karaṇam – Different instruments of action, such as the senses of perception and action. (4) pṛithak cheṣhṭāḥ - Different gestures and body movement. (5) daivam – the unknown factor in all activity, which is beyond human grasp.

In laboratory science experiments, we can predict the result. But life is beyond human calculations. In life, there is Daivam - an unknown, unpredictable factor that makes life beautiful and worth living.

Take the example of aa very successful entrepreneur. In the beginning itself, if he is aware of all the difficulties he has to face in the journey, he may never embark on the journey. The unknown factor and the optimism that the next step may be easier keeps him going.

The basis of Daivam is in the law of karma and the doctrine of reincarnation. Daivam is constituted by our own karmas over many life cycles.

Every action leaves a residual effect (vritti) in our mental system. Many identical vrittis – from similar, repeated actions – solidify a distinct memory block called Samskara. These Samskaras form our character and determine further actions and influence Daivam (the unknown factor).
Positive daivam can be generated by doing unselfish, noble activities, reading of scriptures and through holy associations.

15th verse: “Whatever action we perform with our body, speech and mind – whether it be a right or wrong action, these five factors are involved in those action.”

An action is good if it produces positive daivam. Its opposite is bad action. The 42nd verse of the 18th chapter describe the characteristics of a person who is inclined to do the right action – withdrawing the mind from temptations, sense control, focused on noble causes, internal and external purity, straightforwardness, learn what is worth learning form the empirical world, strong belief that wrong actions do not help in the future.

16th verse: “Those who are with an unrefined intellect and mind identify with the body and have a strong sense of doer ship. They think: “My atma is my body. I should give as much pleasure to this body. They do not understand the daivam aspect.”

This verse is a reference to Charvakas, the school of Indian materialism. They taught: “Might is right. We should not believe what we cannot see with our own eyes. Live in the present - don’t think of yesterday or tomorrow. Don’t think of anything other than giving pleasure to this body.”

The true interpretation of “Living in the present” is grounded in the fundamental impermanence of the empirical world. Due to this impermanence, we should focus on the right actions in the present but with a sense of detachment.

17th verse: “Those whose mind, body, thoughts are refined by listening to spiritual instructions, they are free from the sense of doer ship. They think: “I am not this body. There is a divine element within me.”

18th verse: “Knowledge, the known and the knower – these are the three factors that prompt action. The instrument of action, the action itself and the doer – these are the three constituents of action.”

Any activity is prompted by three factors – the knower, what is to be known and the act of knowing. For example, when one meditates, there are three factors: (1) Dhyata – the one who meditates (2) Dhyeya – the object of meditation and (3) Dhyanam – the act of meditation.

In the 19th verse, Lord Krishna states that knowledge, action and doer have three levels of refinement – sattvik, rajasik and tamasik.

The 20th verse describes the Sattvik nature of knowledge. “That knowledge by which one sees the one supreme reality which is immanent, which is all-pervading, which remains the same without division, which is the indweller in every being, is Sattvik knowledge.”

Whatever divides is inferior. Whatever harmonizes is superior. In spiritual path, one progresses from many to one, from plurality to oneness.

Vedanta accepts plurality. Behind everything, there is one reality. Diversity is the penultimate stage.
Beyond that, at the experience level, there is oneness and unity.

Bhakti is a preparatory stage towards the highest advaitic experience.