18 shakings correspond to the 18 vertebrae of the spine, from the aspect of the body, and all of this is from the aspect of ‘the Tree of Life’. And from the aspect of ‘the Tree of good and evil’: the etrog is likened to the righteous, and the myrtle to the ordinary-ones, and the willow to the wicked.xcSee Vayiqra Rabbah 30:12
And of the Shekhinah it is stated: (Ps. 103:19)... and His Kingdom rules over all, Even though it is stated of Her: (Prov. 3:18) It is a tree of life to them that grasp it, – She rules over the Tree of the Knowledge of good and evil, but from His aspect She is close to King. [Var. and from those aspects, She is at times the female, near to the King]