Kṛṣṇa describes the qualification for steady devotion. He says that people who have acted piously, whose sins are completely finished, and who have freed themselves from the delusion of duality can worship Him with ‘dṛḍha-vratāḥ’, or firm determination. Sin is like dirt on a window; as long as it is there, you cannot see the sun clearly. By acting according to ‘Dharma’ and purifying the heart, the soul clears away the karmic obstacles to vision. When the heart is clean, the mind stops oscillating between like and dislike and finds its focus on the Supreme. This verse emphasizes that spiritual life is not just a mental exercise; it is an ethical one. Our character affects our ability to perceive truth. Kṛṣṇa is encouraging Arjuna that by performing his righteous duty, he is scrubbing away his past sins and preparing himself for that state of unshakable, focused devotion. Purity is the bedrock of spiritual strength.