In plain words
Sva means the Ātma. Svadharma is the very Dharma that belongs to the Ātma. It is not something that changes, nor something that takes on any other form. It is joined to what is beyond qualities and without stain. It is eternally true. It knows no changes and rearrangements. It belongs to the Ātma. That is why we must recognise that men must practise the Dharma that belongs to the Ātma, and that this alone is the highest good. Paradharma means what belongs only to the body. It is bound up with attachment and hatred. It is bound up with Ahaṅkāra and the sense of 'mine'. That is why it is very dangerous. So the Bhagavad Gītā has set them side by side: Svadharma as the highest good, Paradharma as dangerous. That is, by the body's Dharma, some day or other we have to take on this body again to experience this attainment of fruit. All the karmas they do with the body, they do for the sake of gaining fruit. So we must also believe that this is dangerous. At the time we do karmas, we do not understand it at all. We cannot see at all the sorrows that lie ahead. Like rats that rush at the smell of the onion in the trap, we forget what will happen ahead, what will become of it, what lies there.
All the karmas we do for fleeting worldly wealth become, later on, a cause of bondage. But to make this present birth worthwhile, we must try to do good karmas. Here too there are three kinds of karma. All three are bound up with the guṇas. Sāttvika karma, rājasika karma, tāmasika karma. Karmas done with no tie to Ahaṅkāra and the sense of 'mine', without seeking the fruit, every karma for the pleasure of the Lord: these are good karmas. These are karmas full of good qualities, done only to satisfy God, to win God's favour, longing to experience God's love. All karmas done with Ahaṅkāra and the sense of 'mine' and with desire for the fruit are rājasika karmas. These are simply the marks of what ordinary men do every day in this world. Every man born on the earth mostly experiences these karmas of the rājasika kind. We must try to turn them into sāttvika ones. The third is tāmasika karma. It is made of acts such as harming others, hurting others, oppressing others, for nothing but selfishness and self-interest. It goes with the harming of life.