Bg 5.12

yuktaḥ karma-phalaṁ tyaktvā

śāntim āpnoti naiṣṭhikīm

ayuktaḥ kāma-kāreṇa

phale sakto nibadhyate

Word for word: 

yuktaḥ — one who is engaged in devotional service; karma–phalam — the results of all activities; tyaktvā — giving up; śāntim — perfect peace; āpnoti — achieves; naiṣṭhikīm — unflinching; ayuktaḥ — one who is not in Kṛṣṇa consciousness; kāma–kāreṇa — for enjoying the result of work; phale — in the result; saktaḥ — attached; nibadhyate — becomes entangled.

Translation: 

The steadily devoted soul attains unadulterated peace because he offers the result of all activities to Me; whereas a person who is not in union with the Divine, who is greedy for the fruits of his labor, becomes entangled.

 

yuktaḥ- such a person who is well situated and well connected with the spiritual world.

karma-phalaṁ tyaktvā – such a person gives up attachment to the fruits of material world.

śāntim āpnoti -> such a person attains peace , naiṣṭhikīm -> inflatable unshakeable

ayuktaḥ kāma-kāreṇa -> Person who is ayuktaḥ, not connected with absolute truth such a person is kāma-kāreṇa – person acts because of lust, or selfish desire 

phale sakto – person attracted by desire of fruits,  

nibadhyate – such a person becomes bond .

In this verse Sri Krishna is comparing between fruitive workers and karma yogis. In 5.6 also there is comparison between Karma Yogi and Jayan Yogi, there Sri Krishna has said that 

sannyāsas tu mahā-bāho

duḥkham āptum ayogataḥ

yoga-yukto munir brahma

na cireṇādhigacchati

The person who is ayogataḥ, the person who is not practicing Karma Yoga is trying to do inactivity, that person will find it very difficult to become free from bondage, in BG 5.2 Sri Krishna said yes both paths are good but Karma Yoga is better, why? That he has told in 5.6, it is better because ayogataḥ will lead to duḥkham, difficult whereas when one practices yoga activity is natural and one will live happily Sukam Bandat Pramuchayte, but somebody may say that I act, what action causes bondage, this Krishna will explain that it is not action which causes bondage but motivation causes bondage. And if a person doesn’t have selfish motivation then the person will not get bound and Sri Krishna is going to tell over here now in this verse that the person who doesn’t have selfish motivation doesn’t get bound, so here He says 

yuktaḥ karma-phalaṁ tyaktvā – so because this person doesn’t have Selfish motivation that person doesn’t get bound

And when the person doesn’t get bound śāntim āpnoti naiṣṭhikīm, so Sri Krishna knows that Arjuna has longing for peace but He is telling that you will attain supreme peace. He has used Param Shanti in 4.39 and here He is using a similar superlative naiṣṭhikīm which means unshakable very deep unflinching. People may have shown or grown facade of peace in this world but when big agitation will come up, they will also get disturbed but when a person doesn’t have any agitation nothing in the world can disturb him. śāntim āpnoti naiṣṭhikīm. So Sri Krishna is telling Arjuna that don’t think that you will get peace simply by avoiding war, actually even if you avoid the war as long as one has material attachment one will get agitated. But you act in Karma Yoga and purify yourself from material attachment then what you will attain is śāntim naiṣṭhikīm, you will attain unshakable peace.

On the other hand ayuktaḥ, the person who is not connected, so here the comparison is between Karma Yogi and fruitive worker, Karma Kandi or materialist, ayuktaḥ kāma-kāreṇa – such a person works out of material desire, when he works out of material desire what happens? phale sakto nibadhyate – such a person becomes bound. So Krishna is very categorically comparing and explaining what causes bondage is not action but motivation.

When there is kāma-kāreṇa phale sakto there is bondage but when there is yuktaḥ karma-phalaṁ tyaktvā there is no bondage

Srila Prabhupada Purport: This is the secret of Kṛṣṇa consciousness – realization that there is no existence besides Kṛṣṇa is the platform of peace and fearlessness.

Meaning of this: It means ultimately everything is working under the sanction of Krishna and whatever exists is Sri Krishna’s energy, when we see something is separate from Sri Krishna that is illusion, when we see everything is connected to Sri Krishna that is reality. No existence besides Kṛṣṇa is the platform of peace. Peace we talked about which is shanti, but Srila Prabhupada says peace and fearlessness, why fearlessness? naiṣṭhikī, what brings peace is fearlessness, what if that goes off … this fear takes away peace. But when one understands there is nothing beyond Sri Krishna and Sri Krishna is always my well-wisher then there is no loss that is the platform of peace and fearlessness.