In plain words
The religion of Bhārata's people
God, the One of cosmic form, Hiraṇyagarbha: these are not set apart somewhere in some other world. All of them are contained within man. These religions arose for this very purpose: when one has forgotten one's own true home and spent time in a halfway place, to bring one back to one's own home. Many have expounded many meanings for the divine religions of Bhārata, picked it apart, set aside the real truth and believed an untruth full of harm; and so people are seeing to it that this religion has no value of any kind. Religion means bringing one back to one's own home: that is the very nature of religion, its goal. Religion is nothing other than joining God. So people take this Religion to be a harsh punishment built out of some practices or other, some doctrines, some rules. No, no. This religion is the sacred path that reminds us of our own home, which we have forgotten, and brings us back to our own home.
Its sacred inner meaning is “Tat tvam asi”; joining that with this is Tattvamasi. “Prajñānaṃ brahma”; religion is to bring back to memory that divine, that glorious, that ever-new “principle of Prajñāna”. This religion is the very thing that teaches the principle of the Ātma called “Ayaṃ ātmā brahma”. That is, the inner meaning of religion is to lead us to believe that the jīva principle called “I” is the Brahman principle. More than that, “Ahaṃ brahmāsmi”: I myself am going back to join that Brahman, the two are one; teaching this truth is the inner meaning of this religion. That is why the religion of Bhārata's people is the divine path that proves well and truly the authority of the Ṛg, Yajur, Sāma and Atharvaṇa Vedas and brings the jīva principle into oneness with divinity.
Why do Avatāras come?
All the Avatāra principles keep coming down to teach such oneness, to drive away separateness, to make divinity shine forth, to proclaim the principle of the Ātma. To come down as an Avatāra means just this: God descending to the human level. Merely because He comes down to that level, the principle of the Avatāra suffers no stain. Those Avatāras' values do not wane in the least. Here is an example: a little baby is playing on the ground. If the baby's mother, proud that she is the grown-up after all, says to the baby that she will pick it up “if you jump”, can the baby jump? But out of love for the baby, the mother herself bends down and picks the baby up. Merely because the mother bends down, does it mean the mother has given in to the baby? No. So, to bless helpless people who cannot reach the divine state, God takes a human form and comes down to their level. Merely because God takes a human form and comes down to his level, the ignorant man imagines God has given in for his sake alone. Coming in that way is “only bending, not giving in”.
Coming in this way is nothing but the power of God's grace; it is not His giving in and falling under anyone's control. For all time His qualities and sacred powers remain as they truly are, never waning. In whatever places, in whatever circumstances, at whatever times He must reveal whatever kind of power, there He keeps revealing it, in keeping with the influences of that place and time.