Question: What is Ultimate Nirvāṇa (究竟涅槃) in the light of the Great Vehicle’s (大乘: Mahāyāna) teachings?
Answer: The Sanskrit (梵文) word ‘Nirvāṇa’ means ‘extinguishment’ (熄灭) of the metaphorical fires (火) of the three poisons (三毒), of greed, hatred and delusion (贪嗔痴) which we ‘burn’ with. This ‘burning’ represents active disturbing, thus having suffering (苦) of body and mind (身心).
With these poisons eliminated, along with blessings and wisdom (福慧) perfected, there will be the peace and bliss (安乐) of full enlightenment or complete awakening (圆满觉悟) of Buddhahood (佛果), which is the state of perfect calmness (i.e. coolness and stillness) and clarity.
Opposite of the ‘burning’ state, which is flustered and confused, it is also to have total liberation (解脱) from Saṃsāra (轮回), the cycle of (re)birth, ageing, sickness and (re)death (生老病死). With Ultimate Nirvāṇa, there will be the pure aspiration and ability to guide others to Buddhahood too.
The method that most swiftly expedites non-retrogressible (不退转) spiritual progress towards Ultimate Nirvāṇa for the welfare of one and all is the Pure Land Dharma Door (净土法门) of mindfulness of Buddha (念佛). Thus is it taught and specially praised by all Buddhas.
As all other methods in this Dharma-Ending Age (末法时期) cannot match this Dharma Door’s skilful means (方便), Śākyamuni Buddha (释迦牟尼佛) taught us to pay special attention to it. In this era, even basic Nirvāṇa (i.e. not Ultimate Nirvāṇa) of self-liberation is difficult to attain without it.