Musar do Koheleta 1:15

Moreover, as it is written: "The Lord made everything for His own purpose" (Prov. 16:4) (Sabbath 50b).

The reason for Scripture's singling out just these things seems to be this: It is known that every man has 248 physical organs and 365 physical sinews, as it is written (Iyyov 10:11): "With skin and flesh did You clothe me and with bones and sinews did You cover me." Now Scripture mentions skin and flesh and sinews and bones, and calls them only "clothing" and "covering" — "You clothed me"; "You covered me." Whom did He clothe if not the soul that is in his midst — "the essential man." And every organ of the soul is clothed from above with a bodily organ which corresponds to that organ as a garment to the body. And corresponding to this, the Holy One Blessed be He gave us 248 positive commandments and 365 negative commandments. And they are also distributed among the organs. For there is a mitzvah depending on the hand and a mitzvah depending on the foot. And so with all the other organs, as stated in the book of Charedim. And when a man fulfills a mitzvah in this world with a certain organ, in the world to come the light of the L-rd reposes on that organ, and it is that light which vivifies that organ. And so, with each and every mitzvah. It emerges, then, that when a man fulfills the 248 positive commandments, then he is the "complete man," who is sanctified to the L-rd with all of his organs. And this is the intent of what is stated in the section of tzitzith [fringes] (Bamidbar 15:40): "And you will do all My mitzvoth and you will be holy to your G-d." But if, G-d forbid, he be lacking one of the 248 positive commandments, which he has "cast behind his back," and which he did not repent of, there will be a defect in his soul in the world to come in the organ corresponding to that mitzvah. And this is the intent of Berachoth 26a: "(Koheleth 1:15): 'The crooked cannot be made straight' — This refers to one who omitted the Shema of the evening prayer or the Shema of the morning prayer, or the Amidah of the evening prayer or the Amidah of the morning prayer.'" And when a man is careful not to transgress the negative commandments of the Torah, he draws down the light of sanctity upon the sinews of his soul. And if he is not careful, they will be — G-d forbid — defective, as is explained at length in the book, Sha'arei Kedushah, Chapter I.