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.
Evening precedes morning.
Night precedes day. Right at the beginning of the Creation, there is a hint. A hint that this is an evening world. A world of winter and darkness. That's the secret message of Tu B'Shevat, the day when we celebrate new life rising in the tree.