Kṛṣṇa said that what is His mission to come here. Kṛṣṇa is God. He does not require to come here, but He comes to serve some purpose. If God wants to come, nobody can check. Sometimes people question that, "Why God should come?" So our answer is, "Why God should not come?" If He is all-powerful, who can check Him to come here? If we say that God cannot come, that means God becomes under our rules and regulation. So according to Vedic scripture, God comes, and He says personally why He comes: yadā yadā hi dharmasya glānir bhavati (BG 4.7). Whenever there is discrepancies in the prosecution of religious principles, He comes. Yadā yadā hi dharmasya glānir bhavati, abhyutthānam adharmasya. And whenever there is discrepancies in religious procedure, irreligious activities increase. That is natural. Whenever there is lenient government, the rogues and thieves will increase. It is natural. And if the government is very strict, then rogues and thieves cannot become very prominent. So when Kṛṣṇa comes, He has got two business: paritrāṇāya sādhūnāṁ vināśāya ca duṣkṛtām (BG 4.8)—for giving protection to the devotees, to the faithful, and for killing the demons.
So Kṛṣṇa, when He was present, He exhibited these two things. Perhaps you have seen our picture of Nārāyaṇa or Viṣṇu. Viṣṇu has got four hands. In two hands He has got lotus flower and conchshell, and in the other two hands He has got a club and a disc. The disc and club is meant for vināśāya ca duṣkṛtām, for killing the demons and the miscreants. And the conchshell and the lotus flower is meant for giving benediction and blessings to the devotees.
So in the Bhagavad-gītā we understand about Kṛṣṇa. Bhagavad-gītā is a well-read book all over the world. In any country you will find edition of Bhagavad-gītā by the language of the country. So in this Bhagavad-gītā we find that Kṛṣṇa is giving instruction about what is dharma, religion. He says . . . and at the end of His instruction He says, sarva-dharmān parityajya mām ekaṁ śaraṇaṁ vraja (BG 18.66) that, "You give up other types of so-called religious principles. You simply surrender unto Me."