Tu BeShevat is a halachic day in Judaism, marking the cut-off point for tithing produce grown in Eretz Yisroel. It falls on the 15th day of Shevat because it signifies the end of the rainy season, indicating the readiness of crops for tithing.
Beyond the technical and halachic aspects, there is a kabbalistic significance to Tu BeShevat, connecting it to the Aitz HaDa’as Tov v’Ra, [the tree of knowledge for Good and Evil] and the historical sin. The day offers a unique opportunity for Hakores HaTov [recognizing the good] to recognize and give thanks for the abundant gifts of Israel.
Celebrating Tu BeShevat, even in the Diaspora, is encouraged, as it allows one to absorb the significance of the blessings and express gratitude to Hashem for the land’s bounty. This celebration is seen as a way to increase joy in life and counterbalance challenging times.