מדרש אויף דברים 24:19

(Exod. 27:20:) AND YOU SHALL COMMAND THE CHILDREN OF ISRAEL…. This text is related (to Cant. 1:15): AH, YOU ARE BEAUTIFUL, MY BELOVED…. R. Aqiva said: All of the whole world and its fullness was not as worthy as the day on which the Torah of Song of Songs was given to Israel; for while all of the writings are holy, the Song of Songs is the holiest of the holy.¹Yad. 3:5; Tanh., Exod. 8:1; Cant. R. 1:1:11. R. Eleazar ben Azariah said: To what is the matter comparable? To a king who took a se'ah of wheat and gave it to a baker. He said to him: Take from it so much fine flour, so much crushed grain, so much bran. Similarly all the Writings are holy, but the Song of Songs is the holiest of the holy. Rabbi said: See how the Holy One praises the assembly of Israel in it (i.e., in Cant. 1:15). AH, YOU ARE BEAUTIFUL, MY BELOVED. AH, YOU ARE BEAUTIFUL in works.²Cf. Cant. R. 1:15:1. AH, YOU ARE BEAUTIFUL in the work of your ancestors. AH, YOU ARE BEAUTIFUL in the house. AH, YOU ARE BEAUTIFUL in the field. In the house (according to Deut. 6:9): UPON THE DOORPOSTS OF YOUR HOUSE. In the field through priestly shares, tithes, gleaning the forgotten sheaf (of Deut. 24:19), and through the pe'ah (of Lev. 19:9). (Cant. 1:15:) AH, YOU ARE BEAUTIFUL on the roof (according to Deut. 22:8): YOU SHALL MAKE A PARAPET FOR YOUR ROOF. (Cant. 1:15:) AH, YOU ARE BEAUTIFUL in this world. AH, YOU ARE BEAUTIFUL in the world to come.

5) Whence is it derived that he does not pay (for what he ate of the terumah) from shikchah (viz. Devorim 24:19), from peah (viz. Vayikra 19:9), from hefker (what is ownerless), from first tithe whose terumah has been taken, or from second tithe which was redeemed? From "and he shall give to the Cohein the holy thing" — that which can become holy (thus, the signification in the Hebrew).

This is what the verse said: “For they are a graceful adornment for your head [roshekha]” (Proverbs 1:9) – the Rabbis said: Matters of Torah are grace for your infirmity [rashiyutekha]. How so? A learned person, when he grows old, everyone [still] comes and surrounds him and asks him about matters of Torah.
Another interpretation, what is “for they are a graceful adornment [livyat] for your head”? Rabbi Pinḥas bar Ḥama said: Wherever you go, mitzvot accompany [melavot] you. “If you build a new house, you shall make a parapet for your roof” (Deuteronomy 22:8). If you install a door for yourself, mitzvot accompany you, as it is stated: “You shall write them on the doorposts of your house” (Deuteronomy 6:9). If you don new garments, mitzvot accompany you, as it is stated: “You shall not wear a mixture of fibers” (Deuteronomy 22:11). If you go to cut your hair, mitzvot accompany you, as it is stated: “You shall not round the edge of your head” (Leviticus 19:27). If you have a field and go to plow in it, mitzvot accompany you, as it is stated: “You shall not plow with an ox and a donkey together” (Deuteronomy 22:10). If you sow it, mitzvot accompany you, as is stated: “You shall not sow your vineyard with diverse kinds” (Deuteronomy 22:9). If you reap it, mitzvot accompany you, as it is stated: “When you reap your harvest in your field, and you forget a sheaf in the field, [you shall not return to take it]” (Deuteronomy 24:19). The Holy One blessed be He said, [moreover]: ‘Even when you are not occupied with any activity at all, but are [simply] walking on the road, mitzvot accompany you.’ From where is this derived? It is as it is stated: “If a bird's nest will happen before you.”