“שִׂמְחוּ אֶת-יְרוּשָׁלִַם וְגִילוּ בָהּ, כָּל-אֹהֲבֶיהָ; שִׂישׂוּ אִתָּהּ מָשׂוֹשׂ, כָּל-הַמִּתְאַבְּלִים עָלֶיהָ”
“”Be joyful with Jerusalem and rejoice for her, all you who love her; Be exceedingly glad with her, all you who mourn over her,”
“עִבְדוּ אֶת-יְהוָה בְּשִׂמְחָה; בֹּאוּ לְפָנָיו, בִּרְנָנָה”
“Serve YHVH with gladness; Come before Him with joyful singing.”
Jerusalem is the aspect of Malchut and there is joy when there is love and unification with the Light, Zeir Anpin.
The Zohar explains that when we are in exile our relations and connection to YHVH is on a different level, as it says in Psalms 2:11
“עִבְדוּ אֶת-יְהוָה בְּיִרְאָה; וְגִילוּ, בִּרְעָדָה”
“Serve YHVH with awe (fear), and rejoice with trembling.”
When we are close to the Light we are filled with joy because we enjoy the light that fulfills us. Even a poor person or those who experience physical pain can have happiness and joy when they have the faith, trust in the Light that is part of their lives.
Those who are far from the light, which is the aspect of exile, should come to YHVH with fear and awe. Their joy comes with trembling because the light is not strong as strong as for those who are always close to the Light.