These are the three steps of Karmayoga: to do action without the desire for the fruits of action is the first step; to do the work as a sacrifice, as an offering to the Lord is the second step; third, you reach a stage where the work proceeds from the Lord and is passed through you as an instrument, that is the third step.
The third is also called divyam karma. A stage of divyam karma, when you do the divine work, not work for the Divine, but it is divyam karma. In your whole being, since there is no egoistic vibration, since there is no desire, the entire will of the Divine, when it proceeds through you, there is no wave, and therefore there is no scattering away of the will, no distortion of the will; it proceeds straight and with all its force, irresistibly, omnipotently.
This in brief is the entire teaching of Sri Krishna in the first four chapters of the Bhagavad Gita, where what exactly is the action is described and you will see that in this procedure, as we proceed further on, in our path, we become aware of what we are or the world is, or the Supreme is, and therefore, it is a process in which Karma yoga becomes Karmayoga by virtue of the Knowledge. Without the Knowledge, there would be only a mechanical movement, but there is no conscious participation and no conscious understanding, therefore the real Karmayoga would not be possible. That is why, this Karmayoga is supposed to be a union of Karma and Jnana: it is a synthesis of Karma and Jnana.
There is also at the same time an increasing process of devotion; because when you begin to offer yourself to the Lord, then, as you come nearer, and nearer to the Lord, the devotion for the Lord also increases, and therefore in your offering to the Lord, experience of devotion also gets mingled with it.
This last portion is not fully expounded in the first four chapters. That aspect will come much later, when we come to the 11th chapter and the 10th chapter and 12th chapter. And a further exposition will come even much later, because it is a very important element of Bhakti and the culmination of Bhakti, so, at the end of the 18th chapter, when the purity of our instrumentality becomes so great, that sarvadharmān parityajya (XVIII, 66), all Dharma, each Dharma is also an obstacle, each standard of action is also an obstacle, when our entire being becomes so pure, that there is no thought even of Dharma, then the Supreme’s will can pass through us, but that will require a complete offering: mām ekaṁ śaraṇaṁ vraja ( XVIII, 66), a complete offering.
What is described in the 2nd, 3rd, and 4th chapters is ultimately continued to be developed in the 7th, 8th and 9th chapter particularly; how the Knowledge element becomes more and more powerful; and then 10th, 11th, and 12th chapter, we are told how Bhakti becomes very powerful, and then from 13th to 18th chapters we are told as to how absolutely our entire being becomes free from all kinds of Sattwa, Rajas, Tamas, all Gunas and we completely transcends them, then we shall have completed our whole process of Yoga. But in the first four chapters, you might say, the basic foundation of Karmayoga is laid down.