When I was reading Kant and his critics, I could not help but be reminded of Walter Kaufmann's comments on the Gita, in which he objected to the overwhelming pre-eminence of duty for its own sake, excluding all other rewards, which he found a dry and empty approach to life.
Kant also seems to think that if it doesn't hurt, if one doesn't find it a struggle to fight one's instincts in order to obey the categorical imperative of moral duty, then it is of no inherent value. Righteousness is its own reward. Kant does not hold out any transcendental joys, no heaven as compensation, but only a kind of sense of rational justification that comes to one who follows this impersonal categorical imperative. Neither does Kant think much of sentimental human motivation, i.e., love, as a rationale for moral action, for these things belong to the realm of the passions.
Of course, the Upanishads, in the bhūma-vidyā section of Bṛhad-āraṇyaka, state unequivocally the utilitarian principle that happiness is the motivator behind all action. And that therefore we should seek our "enlightened self interest", to again use a phrase from the same school of thought, which is bhūma-sukham, the greatest pleasure. Or, as the Bhāgavatam states: na te viduḥ svārtha-gatiṁ hi viṣṇum, "The foolish do not know that Vishnu is their ultimate self-interest."
We have returned again and again to the statements about the ultimate identity of Self and self (achintya-bheda/abheda): by serving the interests of the Supreme Self, we not only serve our own personal interests, but those of the entire universe. This cannot be proved empirically, but only intuitively, i.e., it has to be taken on faith.
These are fairly Randian, right-wing ideas for me to be espousing, considering that I am a life-long lefty, and still tend to heavily sympathize with the Left. When Thatcher says, "There is no such thing as society: there are individual men and women, and there are families," I cannot help but feel instinctively that she has gone too far. [See this article, which defends Thatcher.] Why bother to include families (or community) if she cannot include the rest of human society? Vasudhaiva kutumbakam, as it were.
The Vaishnava claim is that egoism is common to all. Progressive consciousness sees the widening of self-identification to progressively include various levels of ego-centered consciousness (oral, anal, genital), mental, intellectual, family, community, society, nation, humanity, all creatures, the universe and finally God Himself. yathā taror mūla-niṣecanena... These are all degrees of enlightened self-interest.
The problem with God, philosophically, is that it can be seen as an "empty" concept. Although believers feel God to embody the categorical imperative, we can all project culturally or individually conditioned prejudices onto God. This is a common enough psychological occurrence, and the numerous religions with conflicting values or even the changing values within a particular tradition's history are proof enough of this. In the context of religious apologetics, such an awareness is a great guard against fundamentalism, but it forces us to use reason to examine the values that may have been identified as eternal in particular times and circumstances.
In other words, "God" is a moving goalpost. But don't think that the Gita is not aware of this. As a matter of fact, its acknowledgement of the dialectic of the Absolute and the relative is one of its glorious features. The Gita tells us that we follow socially imposed moral imperatives until our moral sense and self-awareness are sufficiently elevated to bring us to individualization, at which point we are capable of making immediate moral judgements in harmony with the Divine Will. This is the meaning of sarva-dharmān parityājya mām ekaṁ śaraṇaṁ vraja. Becoming free of social conditioning, which has the code-word of varṇāśrama in Hinduism, is the key to moral independence. However, as I mentioned parenthetically in a previous post, it does not mean that one acts contrary to one's socially-conditioned nature. Krishna says that even a wise person acts according to his nature.
So varṇa is about nature, but āśrama is about adhikāra.
When I say "God is a moving goalpost", that does not mean that I am reducing Radha and Krishna, or Chaitanya Mahaprabhu to a psychological construct. First of all, I do consider the choice of iṣṭa-devatā to be a profound step in one's spiritual life. Those who are spiritual dilettantes are not thought much of by Rupa Goswami, nor by me. The choice of iṣṭa-devatā is a crucial step: it is the principal feature of dīkṣā (it is the meaning of divyaṁ jñānam). It is a revelation of self, of our personal psychology, as well as of our profoundest spiritual needs.
The theology of Gaudiya Vaishnavism, and I am principally speaking of Rupa Goswami here, is the first step to understanding the deeper meaning of this choice. Nevertheless, it is important to know that God reveals himself to each of us in a particular way: the Infinite lets himself be known to us, according to our adhikara, so that we can marvel in his glories.
Therefore, Rupa (and other Hindus) will not debate the authenticity of the different forms of God, but it does hierarchize them, it evaluates them, relativizes them. The God of varṇāśrama is bāhya āge koho āra. But the process of hierarchization and relativization implies higher and lower values. The Gita tells us that there are three modes of nature and that a certain kind of faith is true to each of these modes. The Bhagavatam introduces the concept of transcendence, and this is what all this discussion is really about.