The Prime Religious Practice for the Kali-yuga Is the Chanting of the Holy name

The Hare Krsna mantra is specifically mentioned in many Upanisads, such as the Kali-santarano Upanisad, where it is said:
 
hare krsña hare krsna
krsna krsna hare hare
hare räma hare räma
räma räma hare hare
 
iti sodasakam nämnäà
kali -kalmasu-näsanam
näta parataropäya
sarva-vedesu drsyate

"After searching through all the Vedic literature one cannot find a method of religion more sublime for this age than the chanting of Hare Krsña."
                                                                                      Sri Caitanya-caritämåta Ädi-lilä 3.40
 
In Kali-yuga, simply by chanting the holy name one can attain the goal of life:
[Karabhäjana Rsi to Mahäräja Nimi]: " 'Those who are advanced and highly qualified and are interested in the essence of life know the good qualities of Kali-yuga. Such people worship the age of Kali because in this age, simply by chanting the Hare Krsña mahä-mantra, one can advance in spiritual knowledge and attain life's goal.' "
 
This is a quotation from Srimad-Bhägavatam (11.5.36) spoken by the great sage Karabhäjana Rsi, one of the nine Yogendras. The sage was informing Mahäräja Nimi about the people's duty to worship the Supreme Personality of Godhead according to different processes in different yugas.
 
                                                                             Sri Caitanya-caritämåta Madhya-lilä 20.347