Nefesh HaChayim, Reb Itzele's Long Annotation

And to the increasing extent that the three elemental letters alef, mem and shin connect to their roots (as previously mentioned), their light will increase, within them and surrounding them, and the entire body that comes from dust will be purified so that there won’t be any laziness nor heaviness in the limbs/organs of the body. And it will be able to run like the gazelle and be as light as the large bird of prey476Heb.: v’y’hee-yeh rahtz ka-tzvee v’kal ka-nehsher to do the will of the Holy One (blessed be He), as it’s written in Zohar (Pinkhas 225a): “The heart is more pure than all the others; from it comes all the good and the healthiness for all the limbs/organs, and all the strength, all the delight and the wholeness needed for all the limbs/organs”. And in Zohar (Va-yahk-heil 198b): “Come and observe: When a person sets his will in accord with the Master’s service, that will ascends first to the heart, which is the maintainer and the foundation of the entire body. And later that will ascends to all the limbs/organs of the body. The will of the heart and the will of all the limbs/ organs of the body join together as one, and they draw upon themselves the splendor of the Sh’kheena to dwell among them. And that person becomes a part of the Holy One (blessed be He).”