1. After the acarya disappears

    Whenever an acarya comes, following the superior orders of the Supreme Personality of Godhead or His representative, he establishes the principles of religion, as enunciated in Bhagavad-gita. Religion means abiding by the orders of the Supreme Personality of Godhead. Religious principles begin from the time one surrenders to the Supreme Personality of Godhead. It is the acarya's duty to spread a bona fide religious system and induce everyone to bow down before the Supreme Lord. One executes the religious principles by rendering devotional service, specifically the nine items like hearing, chanting and remembering. Unfortunately, when the acarya disappears, rogues and nondevotees take advantage and immediately begin to introduce unauthorized principles in the name of so-called svamis, yogis, philanthropists, welfare workers and so on.

    From Srila Prabhupada's purport to SB 4.28.48