"Therefore Caintanya Mahaprabhu -- not only Caitanya Mahaprabhu but also the Vedic literature -- says:
harer nama harer nama
harer namaiva kevalam
kalau nasty eva nasty eva
nasty eva gatir anyatha
"Kalau means 'in this age.' Nasty eva, nasty eva, nasty eva -- three times nasty eva. Eva means 'certainly,' and nasti means 'not.' 'Certainly not, certainly not, certainly not.' What is that 'certainly not' ? One cannot realize oneself by karma. That is the first 'certainly not.' One cannot realize oneself by jnana. That is the second 'certainly not.' One cannot realize oneself by yoga. Certainly not. Kalau. Kalau means 'in this age.' Kalau nasty eva nasty eva nasty eva gatir anyatha. In this age one certainly cannot achieve success by any of these three methods. Then what is the recommended process ? Harer nama harer nama harer namaiva kevalam. Simply chant the Hare Krishna mantra. Kevalam means 'only.' Simply chant Hare Krishna. It is the easiest and most sublime process. This is recommended, practical, and authorized. So take it. Accept it in any condition of life. Chant. There is no expenditure, there is no loss. We are not chanting a secret. No. It is open. And by chanting you will cleanse your heart."
(Srila Prabhupada, Attaining Perfection)