As it is the duty of the parts of the body to serve the whole, it is the duty of Kṛṣṇa’s devotees to serve Kṛṣṇa as He wants. Kṛṣṇa’s business is to kill the demons, and therefore this should be a devotee’s business also. Because the people of Kali-yuga are fallen, however, Śrī Caitanya Mahāprabhu, out of kindness for them, did not bring any weapon to kill them. Rather, by spreading Kṛṣṇa consciousness, love of Kṛṣṇa, He wanted to kill their nefarious, demoniac activities. This is the purpose of the Kṛṣṇa consciousness movement. Unless the demoniac activities on the surface of the world are diminished or vanquished, no one can be happy. The program for the conditioned soul is fully described in the Bhagavad-gītā, and one simply has to follow these instructions to become happy. Śrī Caitanya Mahāprabhu has therefore prescribed:

harer nāma harer nāma
harer nāmaiva kevalam
kalau nāsty eva nāsty eva
nāsty eva gatir anyathā

Let people chant the Hare Kṛṣṇa mantra constantly. Then their demoniac tendencies will be killed, and they will become first-class devotees, happy in this life and in the next.

Śrīmad-Bhāgavatam 10.1.64, purport