To understand the implications of nibbāna in the present life, it is necessary to know something of the way in which fire is described in the Pali Canon. There, fire is said to be caused by the excitation or agitation of the heat property. To continue burning, it must have sustenance (upādāna). Its relationship to its sustenance is one of clinging, dependence, & entrapment. When it goes out, the heat property is no longer agitated, and the fire is said to be freed. Thus the metaphor of nibbāna in this case would have implications of calming together with release from dependencies, attachments, & bondage. This in turn suggests that of all the attempts to describe the etymology of the word nibbāna, the closest is the one Buddhaghosa proposed in The Path of Purification: Un- (nir) + binding (vāna): Unbinding. [Note: This is quoted from the Intro, the rest is quoted from Chapter 1.]
The discourses report two instances where brāhmans asked the Buddha about the nature of the goal he taught, and he responded with the analogy of the extinguished fire. There is every reason to believe that, in choosing this analogy, he was referring to a concept of fire familiar to his listeners, and, as they had been educated in the Vedic tradition, that he probably had the Vedic concept of fire in mind. This, of course, is not to say that he himself adhered to the Vedic concept or that he was referring to it in all its details. He was simply drawing on a particular aspect of fire as seen in the Vedas so that his listeners could have a familiar reference point for making sense of what he was saying.
Now, although the Vedic texts contain several different theories concerning the physics of fire, there is at least one basic point on which they agree: Fire, even when not manifest, continues to exist in a latent form. The Vedic view of all physical phenomena is that they are the manifestation of pre-existent potencies inherent in nature. Each type of phenomenon has its corresponding potency, which has both personal & impersonal characteristics: as a god and as the powers he wields. In the case of fire, both the god & the phenomenon are called Agni....When fire is extinguished, Agni and his powers do not pass out of existence. Instead, they go into hiding.
The implications of Agni's being an embryo are best understood in light of the theories of biological generation held in ancient India:
The husband, after having entered his wife, becomes an embryo and is born again of her.— Laws of Manu, 9,8
Just as ancient Indians saw an underlying identity connecting a father & his offspring, so too did they perceive a single identity underlying the manifest & embryonic forms of fire. In this way, Agni, repeatedly reborn, was seen as immortal; and in fact, the Vedas attribute immortality to him more frequently than to any other of the gods.
To you, immortal! When you spring to life, all the gods sing for joy... By your powers they were made immortal...[Agni], who extended himself over all the worlds, is the protector of immortality.— RV 6,7
This view that Agni/fire in a latent state is immortal & omnipresent occurs also in the Upaniṣads that were composed circa 850-750 B.C. and later accepted into the Vedic Canon.
....the thought of a fire going out carried no connotations of going out of existence at all. Instead, it implied a return to an omnipresent, immortal state. This has led some scholars to assume that, in using the image of an extinguished fire to illustrate the goal he taught, the Buddha was simply adopting the Vedic position wholesale and meant it to carry the same implications as the last quotation above: a pleasant eternal existence for a tranquil soul.
But when we look at how the Buddha actually used the image of extinguished fire in his teachings, we find that he approached the Vedic idea of latent fire from another angle entirely: If latent fire is everywhere all at once, it is nowhere in particular. If it is conceived as always present in everything, it has to be so loosely defined that it has no defining characteristics, nothing by which it might be known at all. Thus, instead of using the subsistence of latent fire as an image for immortality, he uses the diffuse, indeterminate nature of extinguished fire as understood by the Vedists to illustrate the absolute indescribability of the person who has reached the Buddhist goal.
Just as the destination of a glowing fire
struck with a [blacksmith's] iron hammer,
gradually growing calm,
Even so, there's no destination to describe
for those who are rightly released
— having crossed over the flood
of sensuality's bonds —
for those who've attained
— Ud 8.10