Question: The Midrash notes that the song the Jews sang after they crossed the Red Sea (“Az Yashir”) was unique; its likes had never been heard before in the world. Our Sages even refer to it as a shirah chadashah, a “new song.” What made “Az Yashir” so unique and in what sense was it a “new song”?
Answer: When something good occurs – when a person receives wonderful tidings or achieves great success – he might sing in response. That is a regular type of song.
“Az Yashir” was different. The Targum translates the words in “Az Yashir,” “This is my G-d and I will glorify Him,” as, “I will build Him a Mikdash…and I will serve Him.” This song was not an appreciation of the past but a commitment for the future. The Jewish people saw the future and sang because it looked so glorious.
This type of song – in appreciation of the future – made it “new” and unique.