So the sages in the Naimiṣāraṇya, their inquiry was that, "After departure of Kṛṣṇa, the principles of religion, under whom they are now protected?" Religious principles should be protected. Therefore, Kṛṣṇa's another name is Dharmasetu: He protects. Yadā yadā hi dharmasya glānir bhavati bhārata, tadātmānaṁ sṛjāmy aham (BG 4.7). Just like it is the duty of the state, of the government, to give protection to the department of law and order, similarly Kṛṣṇa, or the Supreme Personality of Godhead, He gives protection to religious principles.
But the world is so deteriorated that Kṛṣṇa comes, He gives protection, makes things in order, leaves His instruction . . . just like when Kṛṣṇa came, He personally supervised the religious principles, and practically, He killed so many demons who were against religious principles. Demons means those who are against religious principles. And He left His instruction, Bhagavad-gītā, how to follow religious principles.
The sum and substance of religious principle is to surrender to God. Sarva-dharmān parityajya mām ekaṁ śaraṇaṁ vraja (BG 18.66). This is religion. Religion means the order given by God. That's all. This is the simple definition of religion. If you, anyone asks, "What do you mean by religion?" religion means to abide by the orders of God. That's all. Just like good citizen means who abides by the order of the government. That's all. There is no difficulty to understand what is good citizen. Whatever the government gives you law, and if you follow, then you are a good citizen. Similarly, there is order by God, and anyone who follows that order, he's religious.