Bhagavad Gita

ಮಯಿ ಸರ್ವಾಣಿ ಕರ್ಮಾಣಿ ಸಂನ್ಯಸ್ಯಾಧ್ಯಾತ್ಮಚೇತಸಾ ।
ನಿರಾಶೀರ್ನಿರ್ಮಮೋ ಭೂತ್ವಾ ಯುಧ್ಯಸ್ವ ವಿಗತಜ್ವರಃ॥೩೦॥
mayi sarvāṇi karmāṇi saṃnyasyādhyātmacetasā |
nirāśīrnirmamo bhūtvā yudhyasva vigatajvaraḥ||30||

Gist of the sloka:
Offering all actions to me, keeping your mind in me, removing ego and attachment, leaving the lethargy, fight.
Lord Krishna instructs Arjuna, dedicate to me all the actions that you do. The word “Sanyasa” has been used here. Sanyasa means – dedicating all the work that has happened through me by Lord grace to Lord as a form of worship. This frame of mind is known as Sanyasa. Naham kartha, Hari kartha; Hari kartha hi kevalam.
One should pray as follows: whatever comes out of my mouth should be as your prayer. Let it be a verse in your praise. Whatever happens in my mind should be your remembrances? Let every action be worship. Lord Krishna is asking Arjuna [and us too] to think along these lines.
The cause of this war was decided about 13 years ago. It was during the time Yudhishthira was performing Rajasuya sacrifice and when Shishupala lost his life. When he asked Lord Vyasa, He had told Yudhishthira that after 13 years there would be a great war. In a way, the war was already predicted, and Lord had willed it. Arjuna was a mere instrument. It is one of the reasons why Lord tells Arjuna to keep his mind on Him, dedicating the actions to Him, proceed for the war.
Our life is a battle. We must do our duty with sincerity. Whatever is the divine plan, it will happen. We cannot change or prevent it from happening. Whatever is the action/duty that the Lord has planned for us, he will ensure we will do it accordingly. We can only dedicate those actions to him, renounce any results/rewards, accept those as blessings and do our duty sincerely. Once a person has this in his mind and action, the responsibility shifts to Lord. We would have no other greater worship than this to offer to Him.
This is the real message that Lord Krishna give it us through Gita.