Arjuna uvaacha:
sannyaasasya mahaabaaho tattvamichhaami veditum |
tyaagasya cha hrisheekesha prithakkeshinishudana || 1 ||

Arjuna said:
O mighty armed, O Hrisheekesha, O slayer of Keshin, I wish to know the difference between sanyaasa and tyaaga.

sannyaasasya: sannyaasa
mahaabaaho : O mighty armed
tattvam : essence
ichhaami : I wish
veditum : know
tyaagasya : tyaaga
cha : and
hrisheekesha : O Hrisheekesha
prithak : difference
keshinishudana : slayer of Keshi
We now commence the eighteenth chapter, which is the final chapter of the Gita. It is the longest chapter, coming in at 78 shlokas. It is a summary of the entire Gita teaching condensed into one chapter. It addresses many topics and themes covered in the entire Gita, and ties up many loose ends as well. It is the most practical among all of the chapters, containing lessons applicable every aspect of our life. Arjuna begins this chapter with a question to Shri Krishna. He wants to know what is the difference between two terms – sannyaasa and tyaaga.
At a superficial level, both the terms have a common meaning which is renunciation. Arjuna probably had come across these terms being used in scriptures or chants, and wanted to know whether there was a difference. But this question is similar to his query in regards to the difference between karma yoga and jnyaana yoga in the third chapter, and the difference between karma yoga and karma sanyaasa in the fifth chapter. Broadly, he wants to know when to act and when not to act. It is a good question because the topic of karma contains many nuances that require clarification and elaboration, which are found in this chapter.
It is interesting to look at the three titles used by Arjuna to address Shri Krishna. Hrisheekesha is one who has conquered the senses. Mahabaaho is one who is mighty armed, one who has tremendous power and energy. Keshinisudana is one who has killed the demon Keshi, who is an enemy. Therefore, only one who has conquered the senses can gain power to destroy one’s internal and external enemies.