The Key Difference Between Mayavada and Bhaktivada
In Śrīmad Bhāgavatam (3.24.31), Kardama says:
Ah! Even though he is beyond the delimitation of form, the All-Attractive appears in such beautiful forms just to delight his own beloved devotees!
The Supreme Being is beyond delimitation, beyond form, and beyond comprehension. However, to enjoy the bliss of love, he delimits himself within infinite forms that come into the comprehension of his devotees. He enjoys doing so because he enjoys the bliss of delighting those who love him.
So, how is this different from māyāvāda?
Māyāvāda claims that "the Supreme Being is beyond delimitation, beyond form, and beyond comprehension.” So does Kardama, representing the bhakti-siddhānta.
Then what is the difference?
Māyāvāda claims that the forms taken by the Supreme Being, such as in his many avatāra, are limitations of him imposed by Māyā (illusion), and he seeks to become free from these limitations and return to his formless state.
Kardama (representing bhakti-siddhānta) makes a very different claim: the forms taken by the Supreme Being, such as in his many avatāra, are accepted by his freewill, as a result of his natural, inherent desire to enjoy bliss by exchanging love with his distinctly manifested energies.
In short, Māyāvāda claims that the Supreme Being has form because it comes under the sway of illusion (Māyā), but Kardama claims that the Supreme Being has form because he enjoys it.
The sum difference between the two claims is that Māyāvāda makes no sense, while Kardama’s bhaktivāda makes very good sense. It makes no sense to suggest that the Supreme Being can come under the sway of anything unpleasant (such as illusion). But it makes very good sense to suggest that the Supreme Being can do anything he pleases by his infinite freewill, in the pursuit of his intrinsic desire to experience bliss.
This is exactly the difference between Māyāvāda and truly Siddhāntik Vedānta.