One who did not get ready for Shabbos by doing teshuvah and good deeds has not prepared a lodging for the Shechinah. The kedushah and Shechinah cannot enter his soul.

Erev Shabbos is, therefore, a time for introspection and teshuvah, so the kedushah of Shabbos can enter and light up one’s soul. A person who does that, palpably feels that “Hashem makes you holy.”

~ Sidduro Shel Shabbos