Bg 3.24

utsīdeyur ime lokā
na kury
āṁ karma ced aham
sa
karasya ca kartā syām
upahany
ām imāḥ prajāḥ

Word for word: 

utsīdeyu — would be put into ruin; ime — all these; lokāḥ — worlds; na — not; kuryām — I perform; karma — prescribed duties; cet — if; aham — I; sakarasya — of unwanted population; ca — and; kartā — creator; syām — would be; upahanyām — would destroy; imāḥ — all these; prajāḥ — living entities.

Translation: 

If I did not perform prescribed duties, all these worlds would be put to ruination. I would be the cause of creating unwanted population, and I would thereby destroy the peace of all living beings.

Utsīdeyur, means disrupted, ime lokā, all these worlds, all these people

na kuryāṁ karma ced aham, if I did not perform my Karma my duties

sakarasya ca kartā syām, so Varna Shankar was Arjuna’s concern in the first chapter, I will become creator of unwanted progeny,  

upahanyām imāḥ prajāḥ, and in this way all the living entities are destroyed.

So here Krishna is gravely pointing out that actually if I did not act responsibly then other people have justification of not acting responsibly and if everyone will start acting irresponsibly then society will crumble.

For example Kshatriya are examples of Chivalry and protection so if they becomes neglectful, irresponsible and if they don’t protect the citizen then who will? And if no one will protect the citizen then they become exploited and if citizen are exploited then what will happen? There will be devastation in society. So therefor Kshatriya has the responsibility to protect people and dharma so Krishna is telling to Arjuna you have this responsibility to protect and if you will not do then unrighteousness will prevail. And if this will happen then ungodly and demonic people will take power and they will exploit society and women that will lead to unwanted progeny and the future generations will be disastrous so this is your responsibility to act in an exemplary way.

Now a question may come up that it is seen that Krishna Himself will not act exemplary e.g.Vrindavan pastimes so (1) one point is that is arena love (2) That time Krishna has not taken position of leadership (3) Srila Prabhupada makes another point in the purport that those who are great people we cannot imitate them, we can admire them, they have powers which we don’t have and Srila Prabhupada quoted from SB here

The Śrīmad-Bhāgavatam (10.33.30–31) afrms:

naitat samācarej jātu
manas
āpi hy anīśvara
vina
śyaty ācaran mauhyād
yath
ārudro ’bdhi-ja viam

īśvarāṇāṁ vaca satya
tathaiv
ācarita kvacit
te
ṣāṁ yat sva-vaco-yukta
buddhim
āṁs tat samācaret

“One should simply follow the instructions of the Lord and His empowered servants. Their instructions are all good for us, and any intelligent person will perform them as instructed. However, one should guard against trying to imitate their actions. One should not try to drink the ocean of poison in imitation of Lord Śiva.”

This answer is given in rasa lila section in SB when Prikshit Maharaj asked how could Krishna danced with other men’s wife? Then Srila Sukadev Goswami answers:

naitat samācarej jātu, samācarej, one should not act like that jātu means certainly.

Manasāpi, even in the mind. anīśvara means those who are not Ishwarh. So those who are not Iswarah should not act like Ishwara even in their mind, why? vinaśyaty ācaran mauhyād, if we act like that vinaśyaty, they will be destroyed, ācaran mauhyād, mauhyād means foolish, they will be destroyed by such an action, and the example is yathārudro ’bdhi-ja viam, rudro means Lord Shiva, ’bdhi-ja means born from ocean, what is born is visam, and Lord Shiva drank this and called Nila Kantha or Kala Kantha (black throat), we cannot do this, so vinaśyaty ācaran mauhyād, so the Mudhas imitate a person like Lord Shiva, vinaśyaty, there will be destruction, now our acharyas has explained that Lord Shiva was not concerned about dyeing why the poison stopped there and didn’t go down even if the poison would have gone down he would not have been affected. But he has checked because he is a Vaishanava, Vaishanava nam yatha Shambu, he is top most of all devotees and he was thinking that my beloved Lord is in my heart so if the poision will go down it will go close to heart and it will cause inconvenience to my Lord who is in my heart. I don’t want to disturb Him I want Him to be present happily in my heart and be happy accepting my devotional services. Same applies with Bhang also, Lord Shiva can drink it we cannot drink it, it is intoxication tamsik, so doing what Lord Shiva has done without authority will simply lead to degradation, so īśvarāṇāṁ vaca satya, we should understand that the words of Ishwar are true,  and tathaivācarita kvacit, how should we act? According to their words, so that means when the Lord or great personalities come to this world that time there action are in two phases, one are those to set an example and others are there to demonstrate His supreme position. Both have important purposes, so for example Lord Ram’s focus was setting example but there are other incarnation their focus is not setting example but demonstrating Their position, like Krishna displaying Virata Rupa, and showing universe in His mouth are made to demonstrate His Supreme Position, So Krishna’s Rasa Lila is also like that . There are laws which all of us has to follow but supreme is superior to the laws, He is not under law, if law was superior to Him than law would be supreme and not Lord, this is not the teachings of vedas but is Karma mimansa principle. Since we are motivated by selfish desire so for us there is law. But Krishna is supremely Pure, Transcendental. He doesn’t have anything to be purified. He is all loving all merciful.