This chapter of 78 verses that deals with the aspects of human behaviour based on the three natures - virtue, passion, and delusion - and the path of selfless action, ends describing the relevance of, and the reverence to, the Gita. While v12 breaks the continuity between v11 and v13 with hyperbolic averments, V41- v48 that describe the allotted duties of man on the basis of his caste are clearly interpolations. In essence, the discourse till v40 is about the human nature and how it affects man and as can be seen, the duties on caste lines detailed in the said interpolations have no continuity of argument.
That apart, v56 combines what is stated in the preceding and the succeeding verses, and thus both are seemingly interpolations. As in earlier chapters, the text acquires continuity if only these verses are bypassed.
V61 avers that the Supreme dwells in humans and deludes them all by his maya. This is contrary to what is stated in Ch5, V14 'It's his nature but not Spirit / Makes man act by wants induced'. Thus, V61 clearly is an interpolation as it contravenes the neutrality of the Supreme Spirit in the affairs of man affirmed throughout by Krishna.
Now scanning the text in the light of the above, first of all, one can note how v12 breaks the continuity between v11 and v13 with hyperbolic averments.
Ch18, V11
Needs one work to sustain life
Relinquients avoid, overloads all
na hi deha-bhṛitā śhakyaṁ tyaktuṁ karmāṇy aśheṣhataḥ
yas tu karma-phala-tyāgī sa tyāgīty abhidhīyate
V12
aniṣhṭam iṣhṭaṁ miśhraṁ cha tri-vidhaṁ karmaṇaḥ phalam
bhavaty atyāgināṁ pretya na tu sannyāsināṁ kvachit
The three-fold fruits of actions—pleasant, unpleasant, and mixed—accrue even after death to those who are attached to personal reward. But, for those who renounce the fruits of their actions, there are no such results in the here or hereafter.
Ch18, V13
Factors five all deeds engulf
Know them well to free thyself
pañchaitāni mahā-bāho kāraṇāni nibodha me
sānkhye kṛitānte proktāni siddhaye sarva-karmaṇām
Hence, v12 as above is an interpolation; moreover it can be seen that the discourse till v40 is about the human nature and how it affects man thus:
Ch18, V36
Make a note of these three ways
Pains which banish 'n fetch bliss.
sukhaṁ tv idānīṁ tri-vidhaṁ śhṛiṇu me bharatarṣhabha
abhyāsād ramate yatra duḥkhāntaṁ cha nigachchhati
Ch18, V37
What fail sprint 'n serve long run
Virtuous know keep woes at bay.
yat tad agre viṣham iva pariṇāme 'mṛitopamam
tat sukhaṁ sāttvikaṁ proktam ātma-buddhi-prasāda-jam
Ch18, V38
It's the way with thy passion
To jump at all that what might tempt
Which would turn sour in due course.
viṣhayendriya-sanyogād yat tad agre 'mṛitopamam
pariṇāme viṣham iva tat sukhaṁ rājasaṁ smṛitam
Ch18, V39
Ever in day-dreams
End up deluded in dreamlands.
yad agre chānubandhe cha sukhaṁ mohanam ātmanaḥ
nidrālasya-pramādotthaṁ tat tāmasam udāhṛitam
Ch18, V40
Beyond the pale of these natures
None ever exists in three worlds.
na tad asti pṛithivyāṁ vā divi deveṣhu vā punaḥ
sattvaṁ prakṛiti-jair muktaṁ yad ebhiḥ syāt tribhir guṇaiḥ
Then, like a bolt from the blue appear the following that describe the allotted duties of man on the basis of his caste with which the readers are already familiar with.
V41
brāhmaṇa-kṣhatriya-viśhāṁ śhūdrāṇāṁ cha parantapa
karmāṇi pravibhaktāni svabhāva-prabhavair guṇaiḥ
The duties of the Brahmins, Kshatriyas, Vaishyas, and Shudras—are distributed according to their qualities, in accordance with their guṇas
V42
śhamo damas tapaḥ śhauchaṁ kṣhāntir ārjavam eva cha
jñānaṁ vijñānam āstikyaṁ brahma-karma svabhāva-jam
Tranquility, restraint, austerity, purity, patience, integrity, knowledge, wisdom, and belief in a hereafter—these are the intrinsic qualities of work for Brahmins.
V43
śhauryaṁ tejo dhṛitir dākṣhyaṁ yuddhe chāpy apalāyanam
dānam īśhvara-bhāvaśh cha kṣhātraṁ karma svabhāva-jam
Valor, strength, fortitude, skill in weaponry, resolve never to retreat from battle, large-heartedness in charity, and leadership abilities, these are the natural qualities of work for Kshatriyas.
V44
kṛiṣhi-gau-rakṣhya-vāṇijyaṁ vaiśhya-karma svabhāva-jam
paricharyātmakaṁ karma śhūdrasyāpi svabhāva-jam
Agriculture, dairy farming, and commerce are the natural works for those with the qualities of Vaishyas. Serving through work is the natural duty for those with the qualities of Shudras.
Having, stipulated the discriminatory caste code, now the interpolators show the carrot and stick to ghettoize the menial at the social fringes thus:
V45
sve sve karmaṇy abhirataḥ sansiddhiṁ labhate naraḥ
sva-karma-nirataḥ siddhiṁ yathā vindati tach chhṛiṇu
By fulfilling their duties, born of their innate qualities, human beings can attain perfection. Now hear from me how one can become perfect by discharging one's prescribed duties.
V46
yataḥ pravṛittir bhūtānāṁ yena sarvam idaṁ tatam
sva-karmaṇā tam abhyarchya siddhiṁ vindati mānavaḥ
By performing one's natural occupation, one worships the Creator from whom all living entities have come into being, and by whom the whole universe is pervaded. By such performance of work, a person easily attains perfection.
V47
śhreyān swa-dharmo viguṇaḥ para-dharmāt sv-anuṣhṭhitāt
svabhāva-niyataṁ karma kurvan nāpnoti kilbiṣham
It is better to perform one's own duty, even imperfectly, rather than indulge in another's work perfectly for by doing one's innate work, a person does not incur sin.
Indeed, the last verse is nothing but a rehash of Ch3, V35, lo, with the same opening line, and it should not be lost on any that this inimical proposition figured the third chapter, the first of the fouled chapters, as well as in the concluding chapter , lest one should forget the rule.
Ch3, V35
śhreyān swa-dharmo viguṇaḥ para-dharmāt sv-anuṣhṭhitāt
swa-dharme nidhanaṁ śhreyaḥ para-dharmo bhayāvahaḥ
It is far better to perform one's natural prescribed duty, though tinged with faults, than to perform another's prescribed duty, though perfectly. In fact, it is preferable to die in the discharge of one's duty, than to follow the path of another, which is fraught with danger.
Now, in this dissection of digressions is this digression –
In the Gita 'as it is', apart from the above Ch3,V35 –Ch18,V47 set of common first-liners, there are three more with the same or nearly same opening lines, and they are
A) Ch 6, V15 'n V28 - yuñjann evaṁ sadātmānaṁ yogī niyata-mānasaḥ and yuñjann evaṁ sadātmānaṁ yogī vigata-kalmaṣhaḥ - the former, as already seen, being an interpolation.
B) Ch9, V34 'n Ch18, V65 - man-manā bhava mad-bhakto mad-yājī māṁ namaskuru and man-manā bhava mad-bhakto mad-yājī māṁ namaskuru, as already noted, the former being an interpolation
C) Ch16, V7 'n Ch18, V30 - pravṛittiṁ cha nivṛittiṁ cha janā na vidur āsurāḥ and pravṛittiṁ cha nivṛittiṁ cha kāryākārye bhayābhaye, both being above board.
Now back to the subject matter with a reiteration of what was stated in v47, jus in case.
V48
saha-jaṁ karma kaunteya sa-doṣham api na tyajet
sarvārambhā hi doṣheṇa dhūmenāgnir ivāvṛitāḥ
One should not abandon duties born of one's nature, even if one sees defects in them, O son of Kunti. Indeed, all endeavors are veiled by some evil, as fire is by smoke.
Putting the caste-centric interpolations behind, the Gita regains its luster with
Ch19, V49
With no want
Allegiant to none,
Freed from action
Thou forsake.
asakta-buddhiḥ sarvatra jitātmā vigata-spṛihaḥ
naiṣhkarmya-siddhiṁ paramāṁ sannyāsenādhigachchhati
Ch18, V50
Leads how forsake to Brahman
Know that Wisdom Supreme now
siddhiṁ prāpto yathā brahma tathāpnoti nibodha me
samāsenaiva kaunteya niṣhṭhā jñānasya yā parā
but only to lose it shortly thereafter.
V56
sarva-karmāṇy api sadā kurvāṇo mad-vyapāśhrayaḥ
mat-prasādād avāpnoti śhāśhvataṁ padam avyayam
My devotees, though performing all kinds of actions, take full refuge in me. By my grace, they attain the eternal and imperishable abode.
As can be seen from the following, in the above verse is combined what is stated in the preceding (Ch18, V55) and the succeeding (Ch18, V57) verses, and thus is an interpolation.
Ch18, V55
It's then one would know Me true
That tends him to be one with Me.
bhaktyā mām abhijānāti yāvān yaśh chāsmi tattvataḥ
tato māṁ tattvato jñātvā viśhate tad-anantaram
Ch18, V57
Let thy faith in Me be strong
Take Me thou for thy shelter
And ever thee act as My agent
chetasā sarva-karmāṇi mayi sannyasya mat-paraḥ
buddhi-yogam upāśhritya mach-chittaḥ satataṁ bhava
Now, over to,
V61
īśhvaraḥ sarva-bhūtānāṁ hṛid-deśhe 'rjuna tiṣhṭhati
bhrāmayan sarva-bhūtāni yantrārūḍhāni māyayā
The Supreme Lord dwells in the hearts of all living beings, O Arjun. According to their karmas, he directs the wanderings of the souls, who are seated on a machine made of the material energy,
which is contrary to
Ch5, V14
It's his nature, but not Spirit
Makes man act by wants induced.
na kartṛitvaṁ na karmāṇi lokasya sṛijati prabhuḥ
na karma-phala-saṅyogaṁ svabhāvas tu pravartate.
Thus, clearly this v61 too is an interpolation as it contravenes the neutrality of the Supreme Spirit in the affairs of man affirmed throughout the text.
Finally, after deliberating upon this proposition, if one comes to the conclusion that the Gita is a work of Vyāsā's genius rather than Lord Krishna revelation, for after all it is the quintessence of the Upanishads, Brahma Sutras, and the Yoga Sastra – all works of man- then, its concluding verse meant to impart divinity to it is an interpolation.
Ch18, V78
Wherever yogic Lord Krishna
Joins hands with great Pārtha
Goddess Victory, spreads carpet
Heaven on earth to set there ever
tach cha sansmṛitya saṁsmṛitya rūpam aty-adbhutaṁ hareḥ
vismayo ye mahān rājan hṛiṣhyāmi cha punaḥ punaḥ
May this 'invocation' paraphrase Krishna's advice to Arjuna,
Ch18, V63
That thee heard of this wisdom
For task on hand now apply mind
iti te jñānam ākhyātaṁ guhyād guhyataraṁ mayā
vimṛiśhyaitad aśheṣheṇa yathechchhasi tathā kuru,
for it to end,
Having perused all of this
Apply mind to grasp it well
To take a call on what is right