What makes this poem the “Song of Songs"?
There are many levels of song. Some sing the Song of their Soul. Within their own soul, they discover everything, their entire spiritual fulfillment.
Others sing the Song of the Nation. They are not contented with the limited circle of the individual soul — it is not expansive enough, not idealistic enough. They aspire to greater heights. With sublime love, they cleave to Knesset Yisrael, Ecclesia Israel. They sing her songs, feel her pains, delight in her hopes, and contemplate her past and her future. With love and wisdom, they contemplate the content of her inner spirit.
Others allow their souls to expand beyond the nation of Israel. They sing the Song of Humanity. They revel in the grandeur of humanity, in the illustriousness of its Divine image. They aspire to humanity’s ultimate goal, and yearn for its sublime perfection. From this source of life, they draw inspiration for their universal thoughts and insights, their aspirations and visions.
And some reach out even higher, until they unite with all of existence, with all creatures and all worlds. With all of them, they sing the Song of the Universe. About this lofty song, the Sages pronounced:
“One who delves in Perek Shirah each day is promised a portion in the World to Come.”
And some succeed in embracing all four songs together. Each songs contributes its unique voice. Together, they harmonize their melodies, giving life and sustenance to the other songs. They continually blend and mix, ringing out with the sound of happiness and joy, the sound of laughter and gladness, the sound of exultation and holiness.
Their culmination ascends to a song of holiness. This is the Song of God, the Song of Israel (the letters ‘ישראל’ may be rearranged to form the words שיר א-ל — the Song of God), in the essence of its power and beauty, truth and greatness. The Song of Songs encompasses together all of these songs — the Song of the Soul, the Song of the Nation, the Song of Humanity, and the Song of the Universe.
“'The Song of Songs, that is Solomon’s [Shlomo]'. The song of the King, the Master of shalom [completeness].” (Rashi, quoting the Midrash on Shir Hashirim 1:1)
(Adapted from Orot HaKodesh vol. II, pp. 444-445)