In plain words
In the eighteen Purāṇas, Vyāsa's words are two: doing good to others is for merit; harming others is for sin.
To put this another way: Help ever, hurt never. We must not cause anyone pain. It is not enough merely not to cause pain. That is, Help ever: we must help others without causing them pain. Is this possible? Surely it is possible. They have taught in many ways about the divine path of Bhakti within humanness. Bhakti is of six kinds. Śānta Bhakti, sakhya Bhakti, dāsya Bhakti, anurāga Bhakti, vātsalya Bhakti, madhura Bhakti. In these six kinds of Bhakti the principle of Prema runs within as a hidden stream. In Prema all are one. Then, the paths of Bhakti are nine:
Listening, singing, remembering Viṣṇu, serving His feet, worship, salutation, service, friendship and the offering of the self.
Only after friendship comes the offering of the self. What is this friendship? What kind of friendship? Hello, Hello how are you? How are you? This is not friendship; heart to heart, love to love. A heart for a heart. Where is this principle of Prema? Where is your friend? Who is your friend? There is money in his pocket. He is in a good position. Till then we keep saying hello, hello. All are friends! After he retires, there is no one even to say goodbye. No, no. God is always right there with you. God is always with you, in you, around you, above you, below you. We must take such a God as our friend. That is precisely why Arjuna, because he took Kṛṣṇa as his friend, went on winning victory in everything. So we must take God as our true friend.