God takes a human form for elevating human beings. There is descent of God for the ascent of man. This is known as Avatara or incarnation of God. In the Gita (IV-6, 7, 8) you will find: "Though unborn, the imperishable Self, and also the Lord of all beings, brooding over nature, which is Mine own, yet I am born through My own power. Whenever there is decay of righteousness, then I Myself come forth. For the protection of the good, for the destruction of evil-doers, for the sake of firmly establishing righteousness, I am born from age to age. "
There are various kinds of Avataras: (1) Poorna-avatara, (2) Amsa-avatara and (3) Avesha-avatara. Lord Krishna was a Poorna-avatara, as you already know, with sixteen rays. Lord Rama was an Avatara of fourteen rays. Sri Sankaracharya was an Amsa-avatara. Avataras generally proceed from Brahma, Vishnu and Siva. They cannot come out of Isvara Himself. Just as a tailor who makes coats for others can make a coat for himself also, God who has created the bodies for others, can create a body for Himself as well. There is no difficulty. He is omnipotent and omniscient. As He has control over Maya, He is fully conscious of His divine nature though He assumes a form. Still He is infinite and unconditioned.
Lord Krishna told Arjuna that this was the ancient and imperishable Yoga which he taught to Vivasvan the Sun-God; Vivasvan taught it to Manu; Manu taught it to Ikshvaku and so it was handed down through Parampara from royal sage to royal sage till it is decayed in the world by great efflux of time and was now renewed for Arjuna as he was His devotee and friend.
Some ignorant persons object: "How can the unborn God assume a human form? How can the Ruler be limited in a perishable, human body? How can the Lord who stands as the Witness only put on a finite body?" These are all vain, worthless, illogical discussions. The doctrine of Avatarahood is perfectly rational, perfectly logical and perfectly tenable. God is the Antaryamin, the Inner Self of all beings. He is not an absolute landlord of this world. He is not extra-cosmic or super-cosmic deity. He pervades and permeates all atoms and the whole universe. He is the Lord of the breath, mind and all organs. In him we live, move and have our very being.
A simple Jivanmukta is like a star that glitters at night. He throws a little light only. Somehow or other he has crossed to the other shore through some Tapas and Sadhana. He cannot elevate a large number of people. Just as the waters of the small spring in the yonder fields can quench the thirst of a few pilgrims only, so also this Kevala Jnani can bring peace for a few persons only. Whereas an Avatara is a mighty person. He is like the big Manasarovar lake. He removes the veil of ignorance of thousands of men and women and takes them to the land of eternal rest, bliss and sunshine.
There are some premonitory signs that indicate the advent of an Avatara. The ground is well prepared for his descent. People take interest in Sankirtana and some pious people disseminate Sankirtana Bhakti far and wide. Some great souls are born beforehand and these train people in selfless service and right conduct.
The Lord incarnated as Nara and Narayana. The object of the incarnation was to teach by precept and example the performance of duty without desire for reward. Nara and Narayana were doing severe penance at Badrikashram. The Lord appeared as a swan to teach Atma-Yoga to Brahma. Dattatreya, the Kumaras, four sons of Brahma are all partial incarnations of Vishnu. Lord Vishnu has taken ten Avataras up till now. Dakshinamoorthy was an Avatara of Lord Siva.
The philosophy of Jesus Christ, the Yogi of Nazareth, is the best of its kind for the European world as is the philosophy of Buddha for Thailand, China, Japan and Sri Lanka. So is the philosophy of Mohammed for Arabia. All are the sons of God made in His image to give to the different parts of the great wide world a message of peace and of the secret of life.
Very few people like Bhishma recognised Lord Krishna as the Avatara. That is the reason why Lord Krishna says: "The foolish disregard Me, when clad in human semblance, ignorant of My Supreme nature, the great Lord of beings. " (Gita: IX-11. ) "Those devoid of reason think of Me, the unmanifest, as having manifestation, knowing not My supreme nature, imperishable, most excellent. " (Gita: VII-24. )
Pseudo-Avataras are abundant these days. They have cropped up like mushrooms. Their disciples pompously advertise these Avataras as Bhagavans, torch-bearers, Perfect Masters, Thakurs, Adepts etc. , for collecting money and building Ashrams for their own comfortable living. They get their downfall also soon. All that glitters is not gold. People have lost their faith now in these charlatans. Truth alone can get victory. How long can falsehood stand? The pseudo-Avataras dress themselves as Lord Krishna with crown and peacock-feathers on their heads and appear before credulous disciples and say: "I am Lord Krishna. Drink my Charanamrita. I shall give you Mukti. " Any saint who wants to rise up should not allow his disciples to advertise. Otherwise he will lose his respect soon. These pseudo-Avataras who live in the midst of utter darkness but profess themselves to be wise and learned, go round and round, deluded in many crooked ways, as blind people led by the blind.
There is grand possibility of the descent of God in human form as an Avatara. This has occurred several times in the past and will continue to occur in future as well. In the divine scheme of things Avataras are indispensably required for the uplift of humanity. In this Kali-Yuga, Kali-Avatara is expected. May that Avatara bring Supreme Joy and Peace to the world. Glory, Glory unto Avataras!