Gita 04.21 explained
śārīraṁ kevalaṁ karma
kurvan nāpnoti kilbiṣam
nirāśīḥ — without desire for the result; yata — controlled; citta–ātmā — mind and intelligence; tyakta — giving up; sarva — all; parigrahaḥ — sense of proprietorship over possessions; śārīram — in keeping body and soul together; kevalam — only; karma — work; kurvan — doing; na — never; āpnoti — does acquire; kilbiṣam — sinful reactions.
Such a man of understanding acts with mind and intelligence perfectly controlled, gives up all sense of proprietorship over his possessions and acts only for the bare necessities of life. Thus working, he is not affected by sinful reactions.
Nirasa in Sanskrit means one without any selfish desire. Asha means having desire in Sanskrit.
Generally we work because we have some desire, but here Krishna is saying what is the reason for a transcendental person to work? It is sarira kavalam karma, at one level it means simply for bodily maintenance he should act, so one may wonder if Arjuna will win the war how he will be doing sariram kevalm karma, he will be living in palace with so much of opulence, we should not be stereotype in sariram kavalm karma, yes we have to act for the maintenance of the body but how we act depends on Varna and ashrama. If one is a Ksheritya he have to live in a way Kshtriya have to live, so Sariram Kavalm Karma will vary for different people, and Kurvan napnoti kilbisam, such a person will not be bound.
Srila Prabhupad in purport mentioned: …for he has no desire for personal sense gratiﬁcation…He moves exactly like a part of a machine. As a machine part requires oiling and cleaning for maintenance, so a Kṛṣṇa conscious man maintains himself by his work just to remain ﬁt for action in the transcendental loving service of the Lord….
Every example has some emphasis here the meaning is not about dehumanizing but as every part in machine work with the whole so we also should be working with the whole. So this will happen by syncing in love with Krishna, we need to understand that we are part.
Srila Prabhupad’s Purport: Like an animal, he has no proprietorship even over his own body. A cruel proprietor of an animal sometimes kills the animal in his possession, yet the animal does not protest.
Again the point is not somebody will slaughter but the point is we should be faithful, like a dog is faithful to master, as a dog lay down his life for master.
Sometime it may appears that Lord is beating us but if we stay fixed to Krishna Consciousness we will understand that Lord has a plan, we should be faithful to the Lord.