Srimad Bhagavatam Canto 12, Chapter 03, Text 52

SB 12.3.52

krte yad dhyayato visnum
 tretayam yajato makhaih
dvapare paricaryayam
 kalau tad dhari-kirtanat
 
Translation: 
 
Whatever result was obtained in Satya-yuga by meditating on Visnu, in Treta-yuga by performing sacrifices, and in Dvapara-yuga by serving the Lord’s lotus feet can be obtained in Kali-yuga simply by chanting the Hare Krsna maha-mantra.
 
Purport: 
 
A similar verse is found in the Visnu Purana (6.2.17), and also in the Padma Purana (Uttara-khanda 72.25) and the Brhan-naradiya Purana (38.97):
 
dhyayan krte yajan yajñais
 tretayam dvapare ’rcayan
yad apnoti tad apnoti
 kalau sankirtya kesavam
 
“Whatever is achieved by meditation in Satya-yuga, by the performance of sacrifice in Treta-yuga, and by the worship of Lord Krsna’s lotus feet in Dvapara-yuga is obtained in the Age of Kali simply by glorifying the name of Lord Kesava.”
 
Srila Jiva Gosvami has further quoted from the Brahma-vaivarta Purana concerning the degraded condition of people in Kali-yuga:
 
atah kalau tapo-yoga-
 vidya-yajñadikah kriyah
sanga bhavanti na krtah
 kusalair api dehibhih
 
“Thus in the Age of Kali the practices of austerity, yoga meditation, Deity worship, sacrifice and so on, along with their various subsidiary functions, are not properly carried out, even by the most expert embodied souls.”
 
Srila Jiva Gosvami has also cited the Caturmasya-mahatmya of the Skanda Purana concerning the necessity of chanting Hare Krsna in this age:
 
tatha caivottamam loke
 tapah sri-hari-kirtanam
kalau yuge visesena
 visnu-prityai samacaret
 
“In this way the most perfect penance to be executed in this world is the chanting of the name of Lord Sri Hari. Especially in the Age of Kali, one can satisfy the Supreme Lord Visnu by performing sankirtana.”
 
In conclusion, massive propaganda should be made all over the world to induce people to chant the Hare Krsna mantra, by which human society can be rescued from the dangerous ocean of the Age of Kali.
 
Thus end the purports of the humble servants of His Divine Grace A.C. Bhaktivedanta Swami Prabhupada to the Twelfth Canto, Third Chapter, of the Srimad-Bhagavatam, entitled “The Bhumi-gita.”
Srimad Bhagavatam Canto 12, Chapter 03, Text 51
Srimad Bhagavatam Canto 12, Chapter 03, Text 19