“The classic metaphor used to describe the Tishrei festivals comes from a verse in the Song of Songs:
‘His left hand under my head, his right arm embraces me.’ (2:6)
The customary explanation is that the left-hand, which is a symbol of rigor and judgment, designates Rosh Hashanah and Yom Kippur.
On Sukkot we are supported by God’s right, the symbol of love.
God’s two “arms” correspond to the architecture of the sukkah.
The law requires that the sukkah have at least two walls, plus the beginning of the third.
This is exactly the form of an embrace.
It is God’s embrace.”
From “The Three Pilgrim Festivals” p. 254, in The Seven Lights by Rabbi Adin Steinsaltz and Rabbi Josy Eisenberg