On the intermediate Shabbat (Shabbat ḥol HaMoed), we read the Song of Songs, which allegorically deals with the love between God and the People of Israel, and on the seventh day, we read The Song of the Sea (Shirat haYam), which Israel sang in praise and thanks to God after He led the Israelites across the Red Sea in safety while drowning the Egyptian pursuers.
Concerning the Song of Songs, our Sages [Zohar Aḥarei Mot 78b] taught: “all the songs are holy, and the Song of Songs is the holy of holies.”
Contrasting the two songs of Pesaḥ allows us to understand Zohar’s comment: the Song of the Sea commemorates an event, which, despite its importance was a one-time event, while the Song of Songs deals with the ongoing relationship between God and His people, from the Exodus until the end of time, and it is therefore "holy of holies." (David Magence)

Shabbat Shalom and Chag Sameach!
The Va’ad