For Man is the tree of the field. When we celebrate Tu B'Shevat, we are not just celebrating the New Year for Trees. In a way, we are celebrating our own re-naissance. We are reminding ourselves that this is just a winter-world. Evening And Morning Winter brings us the shortest days of the year.
Night seems to dominate the day.
Winter is a paradigm of this world. In this world, darkness seems to rule. It's easy to think that this is a brief walk in darkness between two greater darknesses. But to the Jew, this world of darkness is no more than a prelude to a great light. The Jew sees this Winter-world as the harbinger of Spring, not the executioner of Summer.