The first group includes things in nature that require no finishing touches by man. For instance, the air you breathe, the light which shines for you, the beauty which makes you happy, the sweet-smelling scent which refreshes you, etc. This category is symbolized by the myrtle, which has a pleasant aroma, and the esrog, which has aroma and sustenance. The second category comprises things in nature that are inherently beneficial to man, but out of which man has to extract the benefit, i.e. all means of sustenance, which are represented by the lulav, a branch of the date-palm. The third category includes things whose consummation depends entirely upon the hand of man, upon which man exercises his power as their master and from which he extracts all the usefulness that is in them.
Nature supplies only the raw material.
For instance, his dwelling, clothing, utensils, etc., represented in general by wood, i.e. the willow branch , which has no aroma or sustenance. Take them as your very own before Hashem, your G-d. Acknowledge and acclaim that it is G-d who vouchsafes unto you all that is good in life. Cling to them only as the means of living in the presence of G-d according to His will. Rejoice in them before your G-d as the means of fulfilling your duties.