Sin causes one to receive from the external aspects of spirituality:
Regarding idolatry, the Torah states, “And you strayed and served other gods.” Chassidus explains that the word “other” is written as “Achuraim/back,” because idol worship, as well as the performance of any sin for that matter, causes one to nurture from the external levels of holiness. In other words, one is no longer able to receive life force from the internal aspects of Holiness. This is the distance that is created through sin, and one is hence required, through repentance, to tap back into the internal flow of G-dliness. In fact, one of the differences between the soul of a Jew and that of an angel is that the angels derive from the external aspect of G-dliness, G-d’s speech, while the Jewish soul enjoys an internal connection with Hashem, deriving from G-d’s thought. This connection can be damaged, Heaven forbid, through sin, which causes distance between the soul and Hashem.
Many relationships are prone to ups and downs, times of closeness, and occasional times of friction. Every relationship carries responsibilities that have to be performed on behalf of the other, regardless of their current state. A husband must monetarily support his wife, and a wife is obligated to perform certain duties for her husband. During times of closeness, the actions performed by each partner are done with love and a full heart; the person uses his entire soul to truly give to the other. During times of friction, however, the actions are performed out of obligation and necessity, with a cold heart and emotional distance from the receiver. This is a parable of the damage to relationships caused by sin: instead of enjoying a loving bond with Hashem, where He gives to us effusively and graciously out of an inner love for us, we cause ourselves to receive from His external aspects, which simply give out of “necessity,” just as He gives all other creations, even including the side of evil.
 Likkutei Torah p. 64a