Tanya Chapter 38 part 3. The soul of the mitzvah. How intention radiates Divine attachment more than action alone

The intention of attaching to Hashem while performing a mitzvah is like the soul of the mitzvah. It is not that the attachment that is forged by intention is greater than the attachment forged by the act or speech of the mitzvah. Both action and intention are equal in this regard, since they are both the will of Hashem. The difference between them lies in how manifestly this connection is sensed. In just a dry act of the mitzvah, there is minimal radiance of the Divine will. In the intention of the mitzvah, the radiance is profuse. It is like the superiority of the radiance of the soul above that of the body. The body is a vessel and garment for the soul, expressing the soul. The act or speech of the mitzvah is like a body to its intention, which then expresses its core identity –– attachment to Hashem.