Role of Krishna in Bhagavad Gita was that of creator. The doctrine of Bhagavad Gita was given to mankind by Lord Krishna in the battle of Mahabharata between Pandava and Kaurava Kings. The sermon of Bhagavad Gita was given by Lord Krishna to Arjuna to uphold values of dharma (righteousness) against evil forces of adharma (lawlessness). As per Bhagavad Gita Lord Krishna was an avatar of his era (God manifest in human form).
Lord Krishna was the first avatar to have manifested mankind in human form. To provide reprieve to ailing mankind, Lord Krishna gave sermon of Bhagavad Gita that constituted hidden ethical principles of eternal life. In short… knowing teachings contained in Bhagavad Gita human beings finally gained enlightenment in their lifetime. Compared to Bhagavad Gita there is no other scripture available in any religion of world that even compliments Bhagavad Gita.
The sermon of Bhagavad Gita by Krishna had no parallel in mankind. For knowing gist of life… for realizing our true inner self… for reaching God in present life, teachings contained in Bhagavad Gita were necessitated. In present times no human being world over could gain enlightenment without assimilating pearls of wisdom contained in Bhagavad Gita. The 700 shlokas verses contained in Bhagavad Gita were full of jnana (wisdom).
An avatar in Hinduism was one who was a combination of a man god like Mahavira, Gautama Buddha, Jesus Christ or Prophet Mohammed and Chanakya (the most able administrator in the entire history of mankind). To uphold mortal values, Chanakya in a single day rather night eliminated 100 Kings to save lives of millions of countrymen, masses… commoners. As per Bhagavad Gita… still no sin was incurred by Chanakya.
God Almighty through Krishna in Bhagavad Gita states… to save lives of millions, if few evil people are eliminated then no sin is incurred in the process. This is the sublime message of Bhagavad Gita to mankind. As per Krishna in Bhagavad Gita… human beings must always live balanced life… maintaining a delicate balance between right and wrong doings. We sometimes indulged in wrong doings unknowingly. By undergoing penance… we can always undo all wrong doings of past. This is what indulgence in good karma, positive karma all about!
The value of an avatar… messiah… savior must never be underrated. Only when life comes full circle… coming of a messiah, savior is necessitated. As ordained by God Almighty… Satan never wins the end. David always defeats Goliath in the end. No matter how adverse circumstances seem… life in cosmic system was always governed by law of dharma (force of righteousness).
In the battle of Mahabharata, King Duryodhana was very confident that he would win the fight as Bhishma Pitamah (grandfather) and his revered teacher Dronacharya was with him. He also had the support of entire army of Lord Krishna. But King Duryodhana failed to realize that Lord Krishna himself was with Pandava King Arjuna. King Duryodhana underestimated powers of Lord Krishna… an avatar of his era (God manifest in human form)! This was the single biggest mistake of his life that cost him his entire empire.