As you have often pointed out, Buddhist teachings are a vast ocean.
Though some teachings posit a state of nirvana which escapes the cycle of birth and death, many consider nirvana simply as a metaphor similar to Christian heaven; and thus an expedient* teaching designed to motivate people who simply cannot yet believe in their own potential, but who with a high ideal will strive to keep precepts which hopefully will nurture self-esteem.
I prefer the view that life and the Buddha nature inherent in it, like the universe itself are eternal; and that the highest attainment of Buddhism is not personal nirvana, but instead the establishment of a world where greed ignorance and stupidity are rare.
When people ask me what is the goal of Buddhism, I say, “World peace.”
*[Those] Who, despite the
Fail to practice the
Profound and wonderful way
But are perplexed and confused
By a host of troubles —
For these I preach nirvana.
I devise these expedient means and
So cause them to enter into the
The Lotus Sutra Trans. by Burton Watson. Columbia University Press. New York, 1993