Even though a self-realized person has sufficiently purified his heart and need need not perform his prescribed duty, it is for educating the public, ignorant and foolish persons who will consider themselves highly advanced and may imitate the great personalities. Even though Arjuna may perform his duty well when he quits the battle field and lives in the forest by begging like a jnani without performing actions, the common men may consider themselves equal to Arjuna and will fall down. 

Without sufficient purification of the heart one should not abruptly stop the prescribed duties for it may put oneself in a difficult situation. Destruction in the course of one's prescribed duties is better than desrtuction in performing another's duty even perfectly.

"mahajano yena gatah sa panthah" - CC Madhya 17.186. Whatever actions a great man performs, the whole world pursues regardless of what the action is all about. So learned persons should not induce the ignorant mass of people to stop work, rather engage them in Krishna conscious work and gradually help them to attain the state of perfection or Krishna consciousness.

King such as Janaka attained perfection solely by performing prescribed duties. Even Lord Krishna Himself performs prescribed duties when He descends to this world in the human form. He is the Supreme controller and the Supreme Enjoyer, but still to not to bewilder the common men in straying from prescribed duties He does so. 

Sometimes Krishna may act against the prescribed duties with gopis and other devotees. But that is due to the affection He has for His devotees. In any case if Krishna's activities appear different from His words, His words are only to be taken into consideration for we cant imitate His actions anytime.

2. State the three degrees of lust covering the soul together with their respective examples.

1. Fire is covered by smoke - Compared to human beings who can easily invoke the God consciousness with little effort.

2. Mirror is covered by dust - Animals such as birds, beasts who cannot  understand the purpose of life and God consciousness. ( A few exceptions I could think of here are Gajendra and the animals in the dham. There's nothing wrong in being an animal in Spritual world :) . In Mahaprabhu's pastimes, the tigers, deers embracing one another and dancing in ecstasy. Some of the souls in the dham are animals because of offenses in their past lives )

3. Embryo is covered by womb - Trees which almost lost their consciousness or low consciousness which is bound so hard into the material modes of nature.