זאת תורת היולדת בזאת יבא אהרן אל הקודש… (אחרי טז:ג)

An ordinary person is always ready to daven and do mitzvahs, but a tzaddik, after all his preparations, feels broken, thinking, ‘Who am I to stand before Hashem to serve Him?’  This is what the passuk alludes to:  “ואל יבא בכל עת אל הקודש” – his holiness makes him feel unworthy to serve Hashem, therefore he serves Hashem with a broken heart, the passuk tells him “בזאת” –  such a broken heart is the best preparations because through this act “יבא אהרן אל הקודש” – one can reach the most significant level of holiness.