The Torah never uses extraneous words and every Hebrew letter of the Tanakh has infinite meaning. If so, why does this verse use two different expressions to connote happiness: Sasson (ששון), ‘mirth,’ and simcha (שמחה), ‘gladness’? According to Rabbi Mordechai Willig, sasson is the enduring happy feeling of satisfaction and fulfillment. Simcha, on the other hand, refers to an exuberant but temporary experience of joy, felt on special occasions. The feeling of simcha is more intense but short lived, while sasson is less powerful but persists endlessly. Yirmiyahu promises that one day the Land of Israel will be filled with the sweet sounds of both sasson and simcha. Not only will there be intense gladness over the redemption, but the people will experience the long-lasting joy of dwelling permanently in Eretz Yisrael in the presence of God.

Source: Israel in the News