The Upanishads state that Brahman willed and the entire creation inclusive of all the diversity in name, form and function came into existence as His Manifested form, the Brahma Swaroopa. In Vedanta parlance, the word Ishwara refers to the Manifestation of the Unmanifest Supreme Brahman, the Sarguna form of the Nirguna Brahman, which is for purposes of incarnation. In the Gita, Krishna gives a brilliant and compact account of the entire scheme of avatars, pointed out Srimati Rukmini Ramamurthy in a discourse.
He reveals the secret behind His avatars and explains why He takes them as well as how He does so and in what contexts. Krishna explains that He takes various avatars making use of His Prakriti which is synonymous with His Maya Shakti. While all jivatmas are bound by Prakriti and their individual karma and are thus caught in the cycle of birth, the Lord being the Paramatma is beyond all these forces. He is not bound by birth or death, He knows the past, present and future, remaining unchanging in all these phases. He has no beginning or end, is birthless and deathless. Out of His Sankalpa, he takes a human or any suitable form to fulfil certain purposes.
For instance, His presence is needed to restore moral and physical order in the universe whenever there is a decline in dharma and adharma becomes uncontrollable. In such cases, when the welfare of good people is under threat, He steps in to protect them not only from physical harm but also to lead them in the spiritual path. Bali is chastised and given a superior role in Patalaloka. Kaliya is taught a lesson and forgiven. He is freed from the fear of Garuda since His sacred feet have been impressed on his hoods. He is sent from Yamuna to Ramanaka Island. At times, the Lord is severe in the treatment of those such as Hiranyakasipu, Ravana and others.