“In the material world there is always the possibility of deviation from Krishna consciousness, and therefore Krishna and His devotees always act in various forms to curb such godlessness.”
This is from the Srimad-Bhagavatam 8.3.12
[This chapter of the Srimad-Bhagavatam is entitled “Gajendra’s Prayers of Surrender.” In this chapter, the King of the elephants, Gajendra, having been attacked by a crocodile, prayed to the Personality of Godhead for protection.]
I offer my respectful obeisances to Lord Vasudeva, who is all-pervading, to the Lord’s fierce form as Lord Nrsimhadeva, to the Lord’s form as an animal [Lord Varahadeva], to Lord Dattatreya, who preached impersonalism, to Lord Buddha, and to all the other incarnations. I offer my respectful obeisances unto the Lord, who has no material qualities but who accepts the three qualities goodness, passion and ignorance within this material world. I also offer my respectful obeisances unto the impersonal Brahman effulgence.
In the previous verses it has been described that although the Supreme Personality of Godhead has no material form, He accepts innumerable forms to favor His devotees and kill the demons.
As stated in Srimad-Bhagavatam, there are so many incarnations of the Supreme Personality of Godhead that they are like the waves of a river. The waves of a river flow incessantly, and no one can count how many waves there are. Similarly, no one can calculate when and how the different incarnations of the Lord appear according to the necessities of time, place and candidates. The Lord appears perpetually.
As Krishna says in Bhagavad-gita (4.7):
yada yada hi dharmasya
glanir bhavati bharata
tadatmanam srjamy aham
“Whenever and wherever there is a decline in religious practice, O descendant of Bharata, and a predominant rise of irreligion — at that time I descend Myself.” In the material world there is always the possibility of deviation from Krishna consciousness, and therefore Krishna and His devotees always act in various forms to curb such godlessness.