Srimad BhagavadGita

Sri Yāmunāchārya in his Gītārthasaṃgraham described Arjuna's state as asthānasnehakāruṇya dharmādharmadhiyākulaṃ namely 1) misplaced affection, compassion and the resulting pain and 2)deluded state of perceiving own dharma as adharma. So far Kṛṣṇa addressed and corrected these flaws in Arjuna. From now on, Kṛṣṇa will dwell deeper into Arjuna's swa-dharma and how he can rightly execute it. In this śloka Kṛṣṇa tells Arjuna that a kṣatriya like him who knows the distinction between the body and soul and who knows that the soul is eternal and untouched by the characteristics of this body must execute his duty of fighting the war by treating it as his means to mokṣa.

Kṛṣṇa says, "Considering pleasure and pain, gain and loss, victory and defeat alike, if you go ahead and fight the war, you will not be bound in this miserable cycle of life and death."  

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sukha-duḥkhe same kṛtvā The unavoidable experiences of pleasure and pain caused by weapons and events in a war must be treated alike.  

lābhālābhau Our personal gain or loss which causes pleasure or pain respectively should be treated alike.

jayājayau Victory and defeat which cause gain and loss respectively must also be treated alike.

same kṛtvā How can pleasure and pain which are a contrast to each other be treated alike? Treating them alike means neither getting elated by pleasure, gain or victory nor getting dejected by pain, loss or defeat. Those desiring temporary, trivial material benefits blended with misery like owning a kingdom, etc, need not have this equanimous state. In reality temporary benefits which cause pleasure and temporary losses which cause pain, do not affect the soul. The body and soul are different and the soul's ultimate pleasure is attainment of mokṣa alone. When duty is performed with an equanimous attitude towards pleasure and pain, it leads to the attainment of mokṣa. Arjuna expressed lack of interest in the trivial material rewards of this lifetime or the next, like kingdom and its rulership on earth and heaven (kiṃ no rājyena govinda B.G 1.32 and rājyaṃ suraṇām api cādhipatyam) and also surrendered to Kṛṣṇa requesting HIM to instruct about his ultimate benefit (yacchreyaḥ syānniścitaṃ brūhi tan me śiṣyastehaṃ śādhi māṃ tvāṃ prapannam). Therefore Kṛṣṇa advises Arjuna to cultivate such an equanimous attitude towards pleasure and pain.

tataḥ (Thereafter) With this knowledge that victory and gain are not the actual rewards of a war and the realisation of the fact that a righteous war is a kṣatriya's duty, you must certainly arise and fight this war.

yuddhāya yujyasva (Begin the war for the war's sake alone) 

   yuddhāya (for the sake of war) In Sanskṛt grammar, caturthi vibhakti denotes the recipient of an action.

'yuddhāya' is in caturthi vibhakti and this signifies that the war should be fought only for the sake of the war

and not for any other benefits like victory, gain, fame or stay in heaven. This will be explained in detail

by Kṛṣṇa in the ślokas that follow like karmaṇyevādhikāraste mā phaleṣu kadācana B.G 2.47 (You only

have a right to perform the action but no right whatsoever on its reward).

evam If the war is fought in this way with an equanimous attitude...

pāpam na avāpsyasi Pāpam is this saṃsāra- the world of repetitive cycles of birth and death which is full of misery. As it is a known practice to use the word denoting the cause to denote the result too, the term pāpam in this case refers to the misery which is a result of this pāpam (saṃsāra). Mokṣa is when one breaks free from this pāpam i.e this bondage with saṃsāra. 

  A doubt might arise here: Can this word pāpam not be referring to the sin that will be incurred upon killing

Bhīṣma, Droṇa and such others?

Clarification: Even in the absence of an equanimous state towards pleasure and pain, when the war is fought

as a duty with the awareness about the distinction between the body and the soul, no sin will be incurred for

killing Bhīṣma, Droṇa and such others. Here, the pāpam that is said to be destroyed by cultivating an

equanimous state, refers to all the karmas i.e good and bad actions and their resultant reactions which are

destroyed with the practice of prescribed means of liberation like karma yoga, etc. It does not refer to the

relatively lower pāpam (resultant reaction) of killing respectable elders, gurus and relatives. As declared

earlier so’mṛtatvāya kalpate BG 2.15 that a person with such an equanimous state is eligible for liberation,

Arjuna will not only becomes free from any experience of misery in the future, but also be released from the

current state of misery. He will gain eligibility for mokṣa or liberation. 

Summary: 

From Kṛṣṇa's instructions in this śloka it is conclusively learnt that the practice of Karma yoga sprouts jñāna and bhakti and hence it is considered as a means to attain mokṣa.