This week's section is called Ki Tavo (When You Enter). One of the central themes is a series of curses that would befall the Jewish people if they did not observe the precepts of the Torah once they were settled in the Land of Israel. These curses were fulfilled at the time of the destruction of the First Temple.
In the midst of terrible verses, the Torah says (Deuteronomy 28:47), "Because you did not serve the Lord your God with joy and a willing heart in abundance." This verse itself provides one reason (among many) why the curses would occur. It follows logically that God expects us to serve Him—that is, to observe the commandments—with joy. But how does one attain joy? Below is a free translation of a portion of a Rebbe's discourse on how to cultivate joy.
""The matter of joy comes to a person when they feel they possess something, and the greater the thing they possess, the greater the joy. When a person meditates on the fact that a creature is limited, and yet God has given them the possibility of uniting with Him through the observance of the Mitzvot, which is the highest possible elevation, since any level a person can reach is limited and does not at all reach the level of union with the Unlimited Creator, then, since this is the greatest thing anyone can receive, it automatically leads to the greatest joy one can have.".
Moreover, even if a person has fallen and done things contrary to God's will, when he thinks and acknowledges that regardless of his failing, God gives him the opportunity to repent (do teshuvah), through which he will be loved by God just as before the sin, to the point that his sins, once he has corrected them, can be considered as merits, as if he had performed a mitzvah, then, alongside the feeling of bitterness at the time of repentance, there is a very deep feeling of joy in the fact that he did teshuvah and is loved by God again.
It follows, then, that a person can always be joyful, since when he does what God expects of him, he should be happy to fulfill a Mitzvah, and when he fell into sin and realizes that he failed, he begins to repent and should be happy that he did teshuvah and corrected the mistake.
With this idea from the Rebbe, we can also understand that if every commandment should be fulfilled with joy, then the commandment of repentance (teshuvah) should also be accompanied by joy. One should repent with happiness! Although it may sound strange, the idea is as mentioned: the joy of repentance is the power to mend the bond broken by the negative action, the joy that no one will be left out, and that there is always (in the deepest sense of the word, that is, eternally, since God is unlimited in time) another opportunity.
May they be registered and sealed for a good and sweet year,