I think it’s actually a birth canal, wherein good people are reborn for the 2nd time unto glory.
This universe is not our true home. Why then are we here? If men live only one life as Christianity affirms, then perhaps this is a natural place to get one's eternal life started. If, however, as I think, there is something to the doctrines of metempsychosis and suchlike, then we must admit that the main answer is to improve in all of our faculties. But in that case, this universe is somewhat of a simulation: a boot camp for both the soul and the body.