hi Stefos the "Unborn" is certainly one definition of Nibbana but, more simply, the Nikayas also define Nibbana as the cessation of greed, hatred & delusion. therefore, the mind without greed, hatred & delusion experiences the unborn (of non-becoming) and remaining unconditioned by greed, hatred & delusion. the more simple definition of Nibbana may make the more esoteric definition of Nibbana more clear 'Vipassana' means 'clearly seeing' the impermanence (rise & fall; appearance & disappearance), unsatisfactoriness & selflessness of phenomema. Jhana (mental stillness, purity & clarity) enables excellent vipassana to occur because if the mind cannot remain constantly clear, then constantly seeing the impermanence of mental objects cannot occur. Jhana also causes certain mental objects (such as feelings) to manifest in way that is more pronounced than normal and therefore allows the true nature of these mental objects (such as feelings) to be seen more clearly. the 4 brahmaviharas simply (but indirectly) help develop jhana because ill-will/hatred/anger/etc are obstacles to jhana. but to develop jhana, the mind must practise more than just the 4 brahmaviharas. the mind must also practise letting go kind regards