For the coming of the true and complete Redemption! More specifically: there is the prayer, entreaty and supplication that G-d will actually bring the Redemption, imminently and immediately that is said with the feeling of pain and bitterness ("Miryam because of the bitterness") over the length of the exile. [This pain and bitterness] are expressed in the cry from the depths of the heart, "until when, until when, until when!" ... [Together with the cry of pain, the righteous women are (also and essentially) imbued with the feeling of joy; a joy so great that it is expressed in song, because of the greatness of the trust that "Behold he (the king Moshiach) is coming", and he has already come!
(From the talk of Shabbos Parshas Bo, 6 Shvat, and Shabbos Parshas Beshallach, Shabbos Shirah, 13 Shvat, 5752)
