Therefore Rupa Gosvami has introduced this system of regulative principles which I have taught to you also. These regulative principles, such as rising before 4 a.m. for mangala aratrika, chanting 16 rounds minimum on beads daily, reading books, going for the street sankirtana, preaching to anyone and everyone, offering the prasadam, like that, these principles of devotional service are there to safeguard us from maya’s attack by keeping us always enthusiastic. If we strictly observe these principles, we shall remain always enthusiastic. These are the sources and the maintainers of our enthusiasm to serve Krishna. As soon as someone is not following them regularly, it may be certain that his enthusiasm will gradually disappear. Therefore, my request to you is that under any and all circumstances that you yourself shall without fail stick to these principles and make certain that all of the devotees in your charge are also following them strictly.

(From Srila Prabhupada’s letter to Dhananjaya — 31 December 1972)