Bhakti-yoga therefore requires little tapasya, not playthings, tapasya, that "We are addicted to so many sinful activities. We must give it up." That is tapasya. "We must observe fasting on ekadasi day, on Lord's birthday." These are tapasya. If we do not… "We must chant sixteen rounds. We must observe the rules and regulations." This is tapasya. Don't make God very cheap thing: "Oh, it is very cheap thing." No. It has been made very easy for the Kali-yuga people because they cannot undergo any kind of tapasya. There is simple tapasya — "Chant sixteen rounds. Don't take this. Don't do this, four items. Take prasadam. Don't take anything." So nothing is stopped. A little regulated, that this much, if we do not do, then how we can expect to see God and understand God? Tapo divyam [SB 5.5.1]. If simply we remain like hogs and cats and dogs, then how it is possible to realize God? Param pavitram. If I do not become pavitra myself, pure, how I can see the supreme pure? It is impossible. Tapasya must be there. But for this age the tapasya has been minimized.

From Srila Prabhupada's class on Srimad-Bhagavatam 2.9.4 — Japan, April 22, 1972