When Nagarjuna tells us that there is not, essentially, any difference between samsara and nirvana or nirvana and samsara (MMK XXV.19), he opens the door to thinking that, maybe, there is no real difference between a common person and a Buddha, between pain and the end of pain, or a pure mind and a defiled mind.
Nagarjuna's statement doesn't fit well with the Pali Nikayas which dwell at length on the differences between samsara and nirvana. E.g., samsara is always about the cycle of birth and death. Nirvana is the end of this cycle. It is also about immortality. Samsara is about suffering; nirvana is about liberation and bliss.
Whatever Nagarjuna's vantage point was for saying that, essentially, there is no difference between samsara and nirvana or between nirvana and samsara, requires many more words to explain what he meant, in light of what the Buddha said, than he used to compose his tropes.
Scholars who spend a lot of time trying to decipher Nagarjuna's Mulamadhyamakakarika (MMK) will have to admit that these tropes are not even for the likes of the well educated beginner. If one is looking for some profound insight into nirvana or emptiness—please start by reading Zen literature or the Pali Nikayas.
From a pedagogical perspective, Nagarjuna seems to have composed his tropes, not for the average Indian person, but for fellow Buddhist panditas (Buddhist teachers). The negative side of this, Westerners believe Nagarjuna is rejecting gnosis of the transcendent which is not empty. But this is not what Nagarjuna meant by emptiness which best describes conditioned reality that has no core or essence. Our reality is just an empty appearance; so the warning is don't go here; the absolute is not here.
True reality, that is nirvana, according to Nagarjuna in his Mulamadhyamakakarika, is not dependent (apratītya) and not conditioned (anupādāya). Nirvana is not to be found in the phenomenal world or in the psychophysical organism, all this is empty.