The pasuk doesn’t state וְשָׁכַנְתִּי בְּתוֹכָם , “I will dwell in it”. The pasuk states וְשָׁכַנְתִּי בְּתוֹכָם, “I will dwell in them”, in every Yid. Chazal explain that every Yid must construct a spiritual Mishkan in his heart for Hashem’s Shechinah.
The reason it is necessary “וְעָשׂוּ”, that this Mishkan must be built, is due to Adam HaRishon’s sin. The yetzer hara is naturally found in man’s heart, and the Shechinah won’t reside in a place where the yetzer hara has a stronghold. For this reason, the yetzer hara must be removed from the heart. The location that the yetzer hara vacated, is where the Shechinah will reside.
One must be give up at least one personal desire for Hakadosh Baruch Hu, and it needs to be a complete and total renunciation. Otherwise, the yetzer hara – יצר from the word רצון, “desire” – will still hold onto its place in the heart.
IN PRACTICE
A person should choose one of his smaller desires and renounce it entirely for Hakadosh Baruch Hu. When one does so, the person merits that the Shechinah will reside in his heart. With the strength of the Shechinah’s light that is in his heart, it will be easier for him to purify his heart, slowly and gradually, more and more.
