Now Krishna says yes such a person doesn’t need to do any duty, now He will twist this argument and says yeah but there is no reason for him to not do duty also. 

 

Bg 3.18

naiva tasya kṛtenārtho
nākṛteneha kaścana
na cāsya sarva-bhūteṣu
kaścid artha-vyapāśrayaḥ

Word for word: 

na — never; eva — certainly; tasya — his; kṛtena — by discharge of duty; arthaḥ — purpose; na — nor; akṛtena — without discharge of duty; iha — in this world; kaścana — whatever; na — never; ca — and; asya — of him; sarva–bhūteṣu — among all living beings; kaścit — any; artha — purpose; vyapāśrayaḥ — taking shelter of.

Translation: 

A self-realized man has no purpose to fulfill in the discharge of his prescribed duties, nor has he any reason not to perform such work. Nor has he any need to depend on any other living being.

 

naiva tasya kṛtenārtho, kṛten means to do, by discharge of duty artha is purpose; the person has no purpose to fulfill by doing the duty. naiva tasya kṛtenārtho, but then nākṛteneha kaścana, ākṛteneha, at the same time the person has no reason not to do duty also as the person is transcendental so doing duty or not doing duty both are equal why is that? na cāsya sarva-bhūteṣu, such a person for all living beings kaścid artha-vyapāśrayaḥ, artha-vyapāśrayaḥ, such a person is not dependent on other living being. The person doesn’t take shelter of any living being so here Krishna is talking about sarva-bhūteṣu vyapāśrayaḥ, this is not referring to the absolute truth. Here Krishna is not talking about Bhakti, He has not introduced Bhakti so much in this chapter although there is indirect reference to Supreme Lord by Yajna, work for the purpose of Yajna, but there is not direct reference to Mam till now in third chapter so here sarva-bhūteṣu doesn’t include Supreme Lord, yes all of us are dependent on Supreme Lord but here he is not talking about the vertical interaction but the horizontal interaction.

So this person is not a Brahmana, a Brahmana is still part of the society a Brahmana gives knowledge and takes charity, Yajan YaaJan (do Yajan, perform Yajan for others), Pathan, Paathan (read scriptures and teaches others also), Dana (they give charity), Parigraha (the accept charity also), e.g. Dhasrath Maharaj gives his kingdom to Brahmana and they return it back.

So here Krishna is talking about the renounciate who are either Sannyasis (sanyasis are almost out side the Varanasharam) they are top most but from there they are moving further outward. And those who practice Gyana Yoga for attending liberation so they are not taking anything from anyone so they need not give anything to anyone.

SP Purport: explained from devotional perspective: A Kṛṣṇa conscious man does not take shelter of any person – man or demigod. Whatever he does in Kṛṣṇa consciousness is sufficient in the discharge of his obligation.

Which means devotees knows Krishna (as explained earlier one who is a devotee of Krishna is freed from all other types of debts as Krishna is source of everything) a transcendalist may not know Krishna and by the mercy of devotees and Supreme Lord they may develop a clear understanding of what that absolute truth is.