The Rebbe teaches us in Likutei Moharan I 139 that the Mitzvos that we perform don’t actually ascend heavenward until Shabbos comes along, since the powers of evil which have dominance during the week don’t allow it. When Shabbos comes, the evil is nullified and the Mitzvos can then go up.
Reb Noson explains that the negative power that Rebbe is referring to is the unhappiness which we all experience throughout the week which goes away on Shabbos. What gives our Mitzvos the ability to ascend is actually the joy which we take in them. Because of all of what we have to go through on any routine day of our life, we don’t usually find the time or composure to properly appreciate our Mitzvos and to properly delight in them. When Shabbos comes and we finally get a chance to rest from the whole week, our Mitzvos finally get their opportunity to ascend to their proper place.
The Rebbe continues that Hashem then takes each individual Mitzvah which “ascends” to him and takes pleasure and delight in it. The Rebbe emphasizes that this is even regarding the Mitzvos of the smallest and lowest person, even if the person performed the Mitzvah without any thought or anything becoming of a Mitzvah, still, Hashem takes great enjoyment from the Mitzvah.
Of course, once we realize how important it is to be happy with our Mitzvos, we can derive inspiration and motivation to find time every day to really think into our Mitzvos and be joyful about them, not just on Shabbos.
With this in mind we can perhaps understand what the Rebbe means to say in another lesson, Likutei Moharan I 60. The Rebbe teaches that there are people who may spend their days totally engrossed in prayer and Torah study, but Hashem still takes no pleasure in their Avodas Hashem. This is because they are “sleeping” in their Avodas Hashem. What does the Rebbe mean by “sleeping”, and why does Hashem not enjoy Mitzvos done by a person in such a state?
Throughout Likutei Halachos we find Reb Noson referring to a person who feels discouraged as someone who is “asleep”, and when someone uses the encouragement of the Tzaddikim, especially ‘Azamara’, to be happy with his good points, Reb Noson calls it an aspect of “waking up.”
When someone isn’t happy with his Mitzvos, he is sleeping. His Mitzvos can’t go up and Hashem so-to-speak can’t really delight in them.