Musar zu Jirmejahu 31:21

We must remember that though the redemption from Egypt was indeed a great redemption, it was not an ultimate redemption. Such a redemption will occur only in the future when the Messiah comes, at which time the impact of the remaining two letters in G–d's Ineffable Name will also be felt. The fact that during the episode of the Exodus only the first two letters of G–d's Ineffable Name had manifested themselves is alluded to in Exodus 17,16: כי יד על כס י-ה מלחמה לה' בעמלק, which alerts us to the fact that only the first two letters in G–d's Ineffable name carry on the war against Amalek. Our sages have confirmed this when they point to the שירה חדשה, song in the feminine gender, that the Jewish people sung in appreciation of G–d's salvation at that time. This song will be replaced by a שיר חדש, song in the masculine gender, which will be composed and sung by the Jewish people in the future when the final redemption will occur. The redemption from Egypt was rooted in the עולם הנקבות, the "female" world. We read in Jeremiah 31,21 (22) where the prophet speaks about the ultimate redemption, that: ברא השם חדשה בארץ נקבה תסובב גבר, "For the Lord has created something new on earth; a woman courts a man!" This is an allusion to the type of redemption that still awaits us. I have elaborated on this theme in my commentary on the הגדה של פסח. The time of the redemption is the time when all the letters in the Ineffable Name combine and form the dual-faced, male-female Name, i.e. the concept that prevailed at the time the prototype of אדם -who was created male and female combined- was conceived. The prevalent name then was masculine, as is clear from the word אדם as opposed to אדמה.