yad ahańkāram āśritya
na yotsya iti manyase
mithyaiṣa vyavasāyas te
prakṛtis tvāḿ niyokṣyati

Translation of Bhagavad Gita 18.59

If you do not act according to My direction and do not fight, then you will be falsely directed. By your nature, you will have to be engaged in warfare.

Commentary by Sri A.C. Bhaktivedanta Swami Prabhupada of Gaudiya Sampradaya:

Arjuna was a military man, and born of the nature of the kshatriya. Therefore his natural duty was to fight. But due to false ego he was fearing that by killing his teacher, grandfather and friends he would incur sinful reactions. Actually he was considering himself master of his actions, as if he were directing the good and bad results of such work. He forgot that the Supreme Personality of Godhead was present there, instructing him to fight. That is the forgetfulness of the conditioned soul. The Supreme Personality gives directions as to what is good and what is bad, and one simply has to act in Krishna consciousness to attain the perfection of life. No one can ascertain his destiny as the Supreme Lord can; therefore the best course is to take direction from the Supreme Lord and act. No one should neglect the order of the Supreme Personality of Godhead or the order of the spiritual master, who is the representative of God. One should act unhesitatingly to execute the order of the Supreme Personality of Godhead—that will keep one safe under all circumstances.

Commentary by Sri Vishvanatha Chakravarthi Thakur of Gaudiya Sampradaya:

“For me, a ksatriya, the highest dharma is to fight. Being afraid of the sin incurred from killing friends, I do not desire to start fighting.”

The Lord scolds Arjuna in this verse. “Your nature (prakrtih) will make you fight. Now you do not respect my words. But when your irrepressible natural desire to fight arises, then while fighting, and automatically killing your elders like Bhisma, you will smile at me!”

Commentary by Sri Ramanuja of Sri Sampradaya:

18.59 If, in your ‘self-conceit,’ i.e., under a false sense of independence that you know what is good for you and what is not — if, not heeding My command, you think, ‘I will not fight,’ then this resolve based on your sense of independence will be in vain. For Nature will compel you to go against your resolve — you who are ignorant and who adversely react to my sovereignty. He elucidates the same:

Commentary by Sri Sridhara Swami of Rudra Sampradaya:

In a chastising mood the Supreme Lord Krishna states that indulging in ideas not sanctioned by the Vedic scriptures is egotistic vanity and disregarding the injunctions of the Vedic scriptures is delusion. As confirmed earlier the jiva or embodied being is not a free agent. It is subject to the three gunas or modes of material nature which are governed by prakriti the material substratum pervading physical existence. A ksatriya or warrior is situated in raja guna the mode of passion. The influence of raja guna is so strong that by its potency a ksatriya will be compelled to fight by their own volition.

Commentary by Sri Madhvacharya of Brahma Sampradaya:

Lord Krishna is referring to the powerful influence of three gunas or modes of material nature that manifests from prakriti or the material substratum pervading physical existence which is the external potency of the brahman or spiritual substratum pervading all existence. The brahman is the impersonal aspect of the Supreme Lord Krishna. So in this way the Supreme Lord is the absolute power behind all actions.

Commentary by Sri Keshava Kashmiri of Kumara Sampradaya:

Lord Krishna gives the caution that one should not be deluded and think that they are in any way independent of the Supreme Lord. If due to false ego one thinks that they are the independent doer of their actions and take the decision to go against their own natural propensity it would be in vain. Lord Krishna’s external energy is prakriti the material substratum pervading physical existence. From prakriti arises the three gunas or modes of material nature which adjusts itself automatically to the karma or reactions to actions acquired by the different activities a jiva or embodied being performs in countless lifetimes. Changing to the appropriate guna based on such actions the guna itself will compel one to act according to its dictates and any opposition will be futile.

Commentary by Sri Adi Shankaracharya of Advaita Sampradaya:

18.59 Yat, that; manyase, you think, resolve; this-‘na yotsye, I shall not fight’; asritya, by relying; on ahankaram, egotism, mithya, vain; is esah, this; vyava-sayah, determination; te, of yours; because prakrtih, nature, your own nature of a Ksatriya; niyoksyati, will impell; ;tvam, you!

Commentary by Sri Abhinavagupta of Kaula Tantra Sampradaya:

18.41-60 Brahmana – etc. upto avasopitat. Surely the intrinsic nature of the Brahmanas etc., does not voilate what has been difined (above) by way of classifying their duties. Therefore, as far as you are concerned, you have the intrinsic quality of the Ksatriya (warrior), and your nature i.e., intrinsic quality, does, without fail, assume the part of the inciter of yourself, even though you don’t like it. For, a person who acts simply being incited by that (natural condition), there is the strong bondage of the merit or demerit. Therefore, perform actions following the means of correct knowledge, taught by Me. In that case, the bondage would disappear. The intention of the principal sentence (statement of the entire passage under study) is to help to get this idea. The meaning of the subordinate sentences (statements) is evident. Briefly (verse 50) : in short. Knowledge : i.e. the one which has been explained earlier. Nistha conveys, avoiding verbal jugglary, the meaning ‘what has been determined’. He who is endowed with intellect totally pure etc. : All this has been almost explained already. Hence, no more trouble is taken [to comment upon it].

Sanskrit Shloka Without Transliteration Marks:

yad ahankaram asritya
na yotsya iti manyase
mithyaisa vyavasayas te
prakrtis tvam niyoksyati

Sanskrit to English Word for Word Meanings:

yat — if; ahańkāram — of false ego; āśritya — taking shelter; na yotsye — I shall not fight; iti — thus; manyase — you think; mithyā eṣaḥ — this is all false; vyavasāyaḥ — determination; te — your; prakṛtiḥ — material nature; tvām — you; niyokṣyati — will engage.