Text 1

arjuna uvaca
sannyasasya maha-baho
tattvam icchami veditum
tyagasya ca hrishikesha
prithak kesi-nisudana

Translation

Arjuna said: O mighty-armed one, I wish to understand the purpose of renunciation [tyaga] and of the renounced order of life [sannyasa], O killer of the Keshi demon, master of the senses. 

Commentary by Srila Prabhupada 

Actually the Bhagavad-gita is finished in seventeen chapters. The Eighteenth Chapter is a supplementary summarization of the topics discussed before. In every chapter of Bhagavad-gita, Lord Krishna stresses that devotional service unto the Supreme Personality of Godhead is the ultimate goal of life. This same point is summarized in the Eighteenth Chapter as the most confidential path of knowledge. In the first six chapters, stress was given to devotional service: yoginam api sarvesam. .. “Of all yogis or transcendentalists, one who always thinks of Me within himself is best.” In the next six chapters, pure devotional service and its nature and activity were discussed. In the third six chapters, knowledge, renunciation, the activities of material nature and transcendental nature, and devotional service were described. It was concluded that all acts should be performed in conjunction with the Supreme Lord, represented by the words om tat sat, which indicate Vishnu, the Supreme Person. The third part of Bhagavad-gita has shown that devotional service, and nothing else, is the ultimate purpose of life. This has been established by citing past acaryas and the Brahma-sutra, the Vedanta-sutra. Certain impersonalists consider themselves to have a monopoly on the knowledge of Vedanta-sutra, but actually the Vedanta-sutra is meant for understanding devotional service, for the Lord Himself is the composer of the Vedanta-sutra and He is its knower. That is described in the Fifteenth Chapter. In every scripture, every Veda, devotional service is the objective. That is explained in Bhagavad-gita. 

As in the Second Chapter a synopsis of the whole subject matter was described, in the Eighteenth Chapter also the summary of all instruction is given. The purpose of life is indicated to be renunciation and attainment of the transcendental position above the three material modes of nature. Arjuna wants to clarify the two distinct subject matters of Bhagavad-gita, namely renunciation (tyaga) and the renounced order of life (sannyasa). Thus he is asking the meaning of these two words. 

Two words used in this verse to address the Supreme Lord—Hrishikesha and Keshi-nisudana—are significant. Hrishikesha is Krishna, the master of all senses, who can always help us attain mental serenity. Arjuna requests Him to summarize everything in such a way that he can remain equipoised. Yet he has some doubts, and doubts are always compared to demons. He therefore addresses Krishna as Keshi-nisudana. Keshi was a most formidable demon who was killed by the Lord; now Arjuna is expecting Krishna to kill the demon of doubt.

Commentary by Sri Visvanatha Cakravarti Thakur

The eighteenth chapter speaks of the three types of sannyasa, jnana and karma, defines liberation and indicates bhakti as the highest secret of all.

"You stated in the previous chapter 'Uttering the word tat, without seeking results, sacrifices, austerities and charities are performed by those with desire for liberation from the atat material world.' Those with a desire for liberation are sannyasis. But there seems to be others who are detached from all the results of their work, as mentioned by you when you said sarva-karma-phala-tydgam tatah kuru yatatmavan: give up all the result of your work with great attention. (BG 12.11) What is the tyaga of these others?" Wanting to know the distinction, Arjuna asks a question in this verse.

"If the words sannyasa and tydga have different meanings I desire to know the distinct essence of these two. But if they mean the same thing, in your opinion or others' opinion, I desire to know what is that one meaning as well.

"O controller of the senses (hrsikesa), you have made this doubt arise in me since you are the instigator of my intelligence. O killer of Kesi (kesi nisudana), you kill this doubt of mine just as you killed Kesi. O Mighty-armed one (maha baho), you have great strength in your arms, and I have insignificant strength in my arms. You have become friendly with such an expansion as me, rather than with your other expansions with vast knowledge. Therefore I am not afraid to ask this question, since you have become somewhat friendly with me."