Joy Increases Holiness

The Chozeh explained the words of Chazal in Taanis 26b, that when Adar enters we increase joy and when Av enters we decrease joy. When Adar enters we increase through joy, for joy can increase every matter of holiness. When Av enters we decrease through joy, for joy decreases all matters of impurity and negativity, such as the klipos, the husks of impurity. In Av, joy is used to lessen these negative forces.