It’s like the rabbinic nomination of Yom Kippur as Yoma (“The Day”) and Sukkot as HeChag (“The Festival”).
They all have a unique significance: a song above all other songs, a day above all other days, a festival above all other festivals.
Maybe it is the same phenomenon that we find when the Torah (Num. 12:3) calls Moses HaIsh Moshe (“Moses The Man”).
In the case of the Shirah there is a combination of emotion, history and theology to commend its title.
Probably no other song has the feeling and excitement of this song. It vividly re-enacts the emotions of the people – will our Exodus be dashed by recapture by Pharaoh or by drowning in the sea? Will all the centuries’-long yearning for freedom come to nothing? Will God step in and save us? Will we survive and reach the Promised Land?
There is also history; if an event can be said to be the foundation of our identity as a people it is the emergence from the Egyptian episode.
There is theology: God is both our God and the God of our fathers, both Parent and Ruler, both zealous and long-suffering, running His world with both regular patterns and amazing miracles.
What we celebrate in the Shirah is ourselves, our history and our God.