Midrasch zu Dewarim 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).

13) R. Elazar b. Azaryah says: It is written (Devarim 24:19): "When you reap your harvest in your field, if you forget a sheaf in the field, do not return to take it; to the stranger, to the orphan, and to the widow shall it be, so that the L–rd your G d will bless you in all the work of your hands." Scripture (hereby) ordained a blessing for one to whose hand a mitzvah came without his intending it. Derive from this that if a sela were tied in one's garment, and it fell, and a poor man found it, and fed himself with it that Scripture accords him a blessing just as (it does) one who forgets a sheaf in his field.