The answer is that they descend to different planets of the galaxy at the behest of the Lord, to fulfill the role of messiahs there, and to release fallen souls there. On earth, they appear in different places and, in various circumstances, in different climates, they do good for men. But apart from their mission, to wrest from the illusory influence of material energy the embodied and conditioned souls languishing in material existence, they have nothing to do in this world.
Logos 298
Krishna, God, the Supreme Person, and its full emanations, the Avatars, have special signs that distinguish them from ordinary celestial and human beings.
It is written in the Vedas, the original holy scriptures also called “the true gospel”, the eternal gospel which has neither beginning nor end: “All Avatars (incarnations of the Supreme Lord who descend into this world) are plenary emanations of Lord Krishna or emanations of his plenary emanations. But He, Krishna, is God in person, in its most complete original form.”
In order to avoid anyone pretending to be Avatar, let us know that the real Avatar will recognize himself by the particular and characteristic signs of his divinity which he wears on his body, the palm of his hands and the soles of his feet..
Signs of the soles of the Lord's feet: A standard, a lightning bolt, a stick of mahout, a fish, an umbrella, a lotus flower and a disc.
Signs of the palm of his hands: Lotus flowers and wheels.
Seven parts of her body glow reddishly: Her eyes, the palms of her hands, the soles of her feet, her palate, her lips and her nails.
Krishna also has a peacock feather on his hair, and a tuft of white hair on his chest. A large necklace of flowers hangs from his neck. On the other hand, He alone can manifest its gigantic universal form in the material universe, consisting of the entire cosmic manifestation.
If God manifested this universal form, it is precisely to put the fools back in their place, so that one does not take for Avatar that which will be able to manifest this gigantic form as did Lord Krishna. Materialists can therefore, in their own interest, fix their thoughts on this colossal form of the Lord, but that they take care not to be misled by simulators who claim to be the equal of Krishna but who prove incapable of act like Him, or manifest that form that contains the whole universe.