The Torah emphasizes that the underlying reason Klal Yisrael fell prey to the many curses that Moshe enumerated was their lack of joy in mitzvah observance. This is enigmatic! Imagine that one is careful to observe the mitzvos, even punctilious in their observance. Yet, if he lacks “gladness of heart” in performing the mitzvos, he might be subjected to terrible curses. Is this right?
Horav M.D. Soloveitchik, Shlita, distinguishes between two types of sin. The first is represented by the sinner who transgresses and is remorseful about it. He is aware that he did something wrong, that he fell into the clutches of the yetzer hora, evil inclination. In such a case,we hope that he will one day repent his sins and return to Hashem. Unfortunately, a second type is represented by the sinner who is really not concerned with his actions. He does not view his deeds as iniquitous. Indeed, he even “feels good” about what he has done. Such an individual has fallen into an abyss that offers very little hope for his return.
With the above in mind, Horav Soloveitchik presents a homiletic rendering of the pasuk. “Because you did not serve Hashem your G-d,” – How was this lack of service manifest? In what manner was the sin executed? “With gladness and goodness of heart.” There was joy implicit in your transgression. Because it meant nothing to you that you sinned against Hashem, you have created a situation in which hope for teshuvah, repentance, is not realistic. Thus, the curses will befall you. Even in iniquity there is hope, as long as the sinner is remorseful.