In Devarim, Perek 28, Pesukim 45-47, the Torah tells us what it is that brings down the curses that are written in Parashat Ki Tavoh. And the Pesukim say that the reasons why these curses would come upon a person and pursue a person is because the person did not serve G-d with joy. So here, you can see the importance of serving G-d and fulfilling the Mitzvot with happiness, with joy.
The Rabbi from Kutzk (Rabbi Menachem Mendel Morgenstern 1787-1859) is perplexed and questions how the Torah could be so demanding to tell us that if we do not serve G-d with joy then all the curses will come upon us. So one must be on a very high level of spirituality to serve G-d with happiness. But, it is unrealistic for everyone to reach such a level. So he asks why is the Torah requiring such a great level on regular people.
The Rabbi of Kutzk answers by saying that the pasuk might mean something different. Reading with a different punctuation, brings about an entirely different understanding. The explanation discerned says that curses are brought down to those people who are joyful when they do not serve G-d. Such an attitude can not be forgiven. It is unforgivable when one defies the Divine will with an attitude of happiness. Now, of course the Torah recognizes manís fallibility and provides him with the ability to make Teshuva (atonement) which is an opportunity to rectify his sins, however Teshuva requires remorse. Teshuva requires that somebody is truly contrite about his derelict behavior. However, if a person is defiant of the Torah will, and it does not bother him and he does it with happiness, then this is an attitude thatís will bring on all the curses.
This is something thatís attainable by all Jews. Although everyone has sins, we should all at least be bothered that we have committed the sins. At least we should be uncomfortable that we have these sins, and we shouldnít be happy or joyful or complacent that we did wrong. It is a crime according to the Torah if it doesnít bother us at all that we committed a sin.
This time of year, a few weeks before the high holidays, itís a good time to reflect on our bad deeds and more importantly that it should bother us in order to push us to make the proper amends through Teshuva.