Why is the Sankirtan Movement glorious ?

"My dear King, although Kali-yuga is full of faults, there is still one good quality about this age. It is that simply by chanting the Hare Krishna mahä-mantra, one can become free from material bondage and be promoted to the transcendental kingdom." (SB 12.3.51) Those who have accepted the task of spreading the Hare Krishna maha-mantra in full Krishna consciousness should take this opportunity to deliver people very easily from the clutches of material existence. Our duty, therefore, is to follow the instructions of Sri Caitanya Mahäprabhu and preach the Krishna consciousness movement all over the world very sincerely. This is the best welfare activity for the peace and prosperity of human society.
Sri Caitanya Mahäprabhu's movement consists of spreading Krishna-sankirtanam. Param vijayate Sri-Krishna-sankirtanam: "All glories to the Sri Krishnaa sankirtana!" Why is it so glorious? This has also been explained by Sri Caitanya Mahaprabhu. Ceto-darpanam-märjanam: [Cc. Antya 20.12] by the chanting of the Hare Krishna maha-mantra, one's heart is cleansed. The whole difficulty is that in this age of Kali there is no sattva-guna and no clearance of the heart, and therefore people are making the mistake of identifying with their bodies. Even the big philosophers and scientists with whom we deal are practically all under the impression that they are their bodies... Everywhere we find this same misunderstanding. As soon as one is in the bodily conception of life, one is nothing but an animal like a cat or a dog. Thus the most dangerous of the dirty things within our hearts is this misidentification of the body as the self. Under the influence of this misunderstanding, one thinks, "I am this body. I am an Englishman. I am an Indian. I am an American. I am Hindu. I am Muslim." This misconception is the strongest impediment, and it must be removed. That is the instruction of Bhagavad-gita and of Sri Caitanya Mahaprabhu. Indeed, Bhagavad-gitä begins with this instruction:
dehino 'smin yathä dehe
"As the embodied soul continually passes, in this body, from boyhood to youth to old age, the soul similarly passes into another body at death. The self-realized soul is not bewildered by such a change." (Bg. 2.13) Although the soul is within the body, nevertheless, because of misunderstanding and animal propensities one accepts the body as the self. Caitanya Mahäprabhu therefore says, ceto-darpanam-marjanam [Cc. Antya 20.12]. To cleanse the core of the heart, which is full of misunderstanding, is possible only through Sri-Krishna-sankirtana. The leaders of the Krishna consciousness movement should very seriously take this opportunity to be kind to the fallen souls by delivering them from the misunderstanding of materialistic life.

Srimad Bhagvatam, 8.5.23