February 11,2013.Day 167 . BHAGAVAD GITA - As It Is.Original by His Divine Grace Srila Prabhupada. Chapter 4.TEXT 8

Chapter 4. Transcendental Knowledge

TEXT 8

paritranaya sadhunam
vinasaya ca duskrtam
dharma-samsthapanarthaya
sambhavami yuge yuge

SYNONYMS

paritranaya--for the deliverance; sadhunam--of the devotees;vinasaya--for the annihilation; ca--also; duskrtam--of the miscreants;dharma--principles of religion; samsthapana-arthaya--to reestablish;sambhavami--I do appear; yuge--millennium; yuge--after millennium.

TRANSLATION

In order to deliver the pious and to annihilate the miscreants, as well as to reestablish the principles of religion, I advent Myself millennium after millennium.

PURPORT

According to Bhagavad-gita, a sadhu (holy man) is a man in Krsna consciousness. A person may appear to be irreligious, but if he has the qualifications of Krsna consciousness wholly and fully, he is to be understood to be a sadhu. And duskrtam applies to one who doesn't care for Krsna consciousness. Such miscreants, or duskrtam, are described as foolish and the lowest of mankind, even though they may be decorated with mundane education; whereas another person, who is one hundred percent engaged in Krsna consciousness, is accepted as sadhu, even though such a person may neither be learned nor well cultured. As far as the atheistic are concerned, it is not necessary for the Supreme Lord to appear as He is to destroy them, as He did with the demons Ravana and Kamsa. The Lord has many agents who are quite competent to vanquish demons. But the Lord especially descends to appease His unalloyed devotees, who are always harassed by the demoniac. The demon harasses the devotee, even though the latter may happen to be his kin. Although Prahlada Maharaja was the son of Hiranyakasipu, he was nonetheless persecuted by his father; although Devaki, the mother of Krsna, was the sister of Kamsa, she and her husband Vasudeva were persecuted only because Krsna was to be born of them. So Lord Krsna appeared primarily to deliver Devaki, rather than kill Kamsa, but both were performed simultaneously. Therefore it is said here that to deliver the devotee and vanquish the demon miscreants, the Lord appears in different incarnations. 
In the Caitanya-caritamrta of Krsnadasa Kaviraja, the following verses summarize these principles of incarnation:

srsti-hetu yei murti prapance avatare
sei isvara-murti 'avatara' nama dhare

mayatita paravyome sabara avasthana
visve avatari' dhare 'avatara' nama

"The avatara, or incarnation of Godhead, descends from the kingdom of God for material manifestation. And the particular form of the Personality of Godhead who so descends is called an incarnation, oravatara. Such incarnations are situated in the spiritual world, the kingdom of God. When they descend to the material creation, they assume the nameavatara." 
There are various kinds of avataras, such as purusavataras, gunavataras, lilavataras, sakty-avesa avataras, manvantara-avataras and yugavataras--all appearing on schedule all over the universe. But Lord Krsna is the primeval Lord, the fountainhead of allavataras. Lord Sri Krsna descends for the specific purposes of mitigating the anxieties of the pure devotees, who are very anxious to see Him in His original Vrndavana pastimes. Therefore, the prime purpose of the Krsnaavatara is to satisfy His unalloyed devotees. 
The Lord says that He incarnates Himself in every millennium. This indicates that He incarnates also in the age of Kali. As stated in the Srimad-Bhagavatam, the incarnation in the age of Kali is Lord Caitanya Mahaprabhu, who spread the worship of Krsna by the sankirtana movement (congregational chanting of the holy names), and spread Krsna consciousness throughout India. He predicted that this culture of sankirtana would be broadcast all over the world, from town to town and village to village. Lord Caitanya as the incarnation of Krsna, the Personality of Godhead, is described secretly but not directly in the confidential parts of the revealed scriptures, such as the Upanisads, Mahabharata,Bhagavatam, etc. The devotees of Lord Krsna are much attracted by thesankirtana movement of Lord Caitanya. This avatara of the Lord does not kill the miscreants, but delivers them by the causeless mercy of the Lord.