The Song of the Sea (Ex 15:1-22) gives voice to the victory of the Children of Israel over the Egyptians after 400 years of slavery. It took place on the 8th day after leaving Egypt, the day of renewal, the day of covenant with God. When this passage is read in synagogue, the entire congregation stands up in recognition of this event. It is also the first occasion in the Torah that we find joyousness expressed through singing and dancing. Let us examine aspects of this event in detail. It is written:
Thus, the Lord saved Israel on that day from the hand of the Egyptians; and Israel saw the Egyptians dead upon the seashore (Ex. 14:30).
Then:
And Miriam the prophetess, the sister of Aaron, took the tambourine in her hand; and all the women went out after her with tambourines, dancing (Ex. 15:20).
Various questions arise from these two verses: Why does it say, ‘on that day’ very definitively and why does the text state ‘Miriam the Prophetess’? What did she prophesy? Many rabbinical texts have discussed this point, but few have come to a satisfactory conclusion. The secret is in the 'tambourine'. If we look at the Hebrew text we see that Miriam not only took up the tambourine, but it says THE tambourine et ha tof את התף where grammatically the word et is emphatic, pointing to not just a tambourine but the specific tambourine.
All these questions are answered in I Kings 6:1
And it came to pass in the four hundred and eightieth year after the people of Israel came out of the land of Egypt, in the fourth year of Solomon's reign over Israel, in the month Ziv, which is the second month, that he began to build the house of the Lord.
The word for drum, tof, is spelled taf-peh תף whose gematrical value is 80+400=480. Hence Miriam, by taking up Et ha Tof ‘the drum’ was a prophetess because she was using the drum to announce the future construction of the Temple 480 years later under King Solomon. It was 'on that day', the number of years from the 8th day after the the First Passover, that the construction of the temple by Solomon began.
The joyousness of singing and dancing was because the Children of Israel realized that, as Moses had stated each time he confronted Pharaoh saying Let my people go, that they may serve Me, freedom was to become to a reality. Indeed, the greatest event in Jewish history after entry into the Promised Land was the construction of Solomon’s Temple: a home for the Lord God of the Hebrews who entered the sanctum in a cloud:
And that the priests could not stand to minister because of the cloud; for the glory of the Lord had filled the house of the Lord (I Kings 8:11).