Here's an attempt at a "non-religious" description of vipassana. A "religious" definition talks about an improved fundamental understanding of reality, which explicitly or implicitly portrays advanced vipassana practitioners as beings on a higher, somehow more conscious level than ordinary humans.
Vipassana is essentially dying. The goal of vipassana is a simulated death. This is achieved by tricking the mind temporarily into not treating any qualia as self.
This helps overcome fear of death through familiarity and practice. In addition, the process of meditation by necessity improves concentration, mindfulness, and the ability to let go of stuff. These are all useful skills so vipassana is probably not a waste of time.
Overcoming the fear of death can be done through other means, like exposing yourself to danger or self-inducing fainting. Near-death experiences also give you the practice and familiarity. Deaths of people close to you may give some empathetic familiarity as well.
Likewise, concentration, mindfulness, and the ability to let go of stuff can of course be trained by other methods, and it's not clear how useful or effective could improvement in these areas possibly be, anyway.
