Tanya Chapter 39 part 7

Knowing the difference can make all of the difference. By analyzing the reward for a mitzvah and being aware of its destination in the spiritual worlds, we can understand something of the essential make-up of a mitzvah. Knowing that a mitzvah powered by love and fear ascends to the higher worlds and becomes incorporated within the ten holy sefirot motivates us to serve Hashem out of a space of awareness and connection. On the other hand, while every act of Torah and mitzvah is inherently holy, a mitzvah done without love and fear lacks the power to ascend to the holy sefirot.