In the context of a Jew's relationship with G-d, every sin is an act of betrayal. Thus, teshuvah (repentance) is the act of restoring closeness after the bonds of trust have been broken.
Although we normally shun depression and strive to be joyous all the time, there is an appropriate context for sadness. When is there a benefit to having a broken heart?
Are the darkest moments of our lives really G-d communicating with us on a higher level? The traditional prayer of mourning -- "Baruch Dayan Emet" -- holds the answer.
Sometimes we cannot get inspired because our hearts are callous from past sins. Even if we have repented in the past, if we are about to ascend to a higher level of spiritual growth, we need to tap into a deeper level of repentance.
G-d is not displeased with those who struggle to do the right thing. To the contrary, it causes G-d great pleasure to see us striving to overcome our lower nature.