/lit/ - Literature

>Having become separated from sensual desire, having become separated from nonvirtuous qualities, a monk enters into and abides in the first concentration, in which there is conceptuality and analysis, which has joy and bliss, and which arises from separation from hindrances . . . . Due to diminishment of conceptuality and analysis, he enters into and abides in the second concentration, has internal tranquility and has one-pointed concentration of thought, devoid of conceptuality and analysis, but having joy and bliss . . . . Due to detachment from joy, the monk dwells in equanimity, has mindfulness and clear understanding, experiencing bliss in mind and body. . . . Through eliminating both pain and pleasure, and due to previous disappearance of sorrow and happiness, the monk enters into and abides in the fourth concentration, devoid of pain and pleasure, a state of equanimity and absolute purity of mindfulness.
- Quotation from the Dīgha Nikāya present in "Introduction to Tibetan Buddhism", by John Powers.

Okay, that's really interesting. This is the great division between Buddhism and most of Hinduism: i.e., Buddhism aims at Nirvāṇa; Hinduism aims at what Buddhism calls Arūpa-dhātu (Formless Realms). This is no problem at all if you are a Theravāda practitioner/scholar.
Now, assuming Mahāyāna (which is my field of interest) is right and that there are such things as (a) a Buddha-Nature (Tathāgatagarbha) and (b) Pure Lands (Buddhakṣetra), I would like to come up with some doctrinal questions:

1- How is the (a) Tathāgatagarbha any different from the idea of an Ātman (in the purest sense of the idea in Hinduism)? (i.e., how is the Buddha-Nature any different from the Self, which, according to the Dṛg-Dṛśya Viveka, is not identical to the ego nor to the mind and which is unknowable?) From what I know the two terms are used in an interchangeable way in the Mahāyāna Mahāparinirvāṇa Sūtra, which makes things even trickier.
2- If there are Arūpa-dhātus which, in their peak, neither form, nor bliss, nor joy even exist, why would someone even "take rebirth" in a Buddhakṣetra (Pure Land)? That considering that, from what I know, a Pure Land is identical to Nirvāṇa in some traditions of Tibetan Buddhism. Also, why would the Garbhakoṣadhātu (Womb Realm) and the Vajradhātu (Diamond Realm) even exist and not be Formless Realms?