Source: 'Complete Works of Swami Vivekananda' - Volume 3- Bhakthi Yoga-
CHAPTER VI INCARNATE TEACHERS AND INCARNATION:
"Wherever His name is spoken, that very place is holy. How much more so is the man who speaks His name, and with what veneration ,ought we approach that man out of whom comes to us spiritual truth! Such great teachers of spiritual truth are indeed very few in number in this world, but the world is never altogether without them. They are always the fairest flowers of human life "the ocean of mercy without any motive". "Know the Guru to be Me", says Shri Krishna in the Bhagavata. The moment the world is absolutely bereft of these, it becomes a hideous hell and hastens on to its destruction."
God understands human failings and becomes man to do good to humanity:
"Whenever virtue subsides and wickedness prevails, I manifest Myself. To establish virtue, to destroy evil, to save the good I come from Yuga (age) to Yuga."
"Fools deride Me who have assumed the human form, without knowing My real nature as the Lord of the universe." Such is Shri Krishna's declaration in the Gita on Incarnation.
"When a huge tidal wave comes," says Bhagavan Shri Ramakrishna, "all the little brooks and ditches become full to the brim without any effort or consciousness on their own part; so when an Incarnation comes, a tidal wave of spirituality breaks upon the world, and people feel spirituality almost full in the air."