The gemara (Sotah 12b) records a dispute regarding on which day Moshe Rabeinu as a baby was placed in the Nile. One opinion holds it was the 21st of Nisan, and the Malachim protested to G-d that it would be unjust for baby Moshe to come to harm on the very day that he would later recite shirah [i.e. Shiras haYam]. Another view holds it was the 6th of Sivan, and the Malachim protested that it would be unjust for baby Moshe to come to harm on the very day he would later receive the Torah.
The Shem m’Shmuel explains that this machlokes is not just a matter of chronology. The miracle of Yam Suf took place in response to the initiative - the isreusa d’letata - of Bnei Yisrael and the Shirah was their composition. Kabbalas haTorah was G-d reaching out to Bnei Yisrael - isre’usa d'l'eila – to bestow upon us His “composition”. With which event do we associate Moshe? Is he the passive recipient of G-d’s law, or his he the driving force behind Bnei Yisrael’s development as a people? When we consider the Shiras haYam vs. “kisvu lachem es hashirah hazos” [referring to Torah], which song are we singing? Is religion about passive acceptance of boundaries, or creative initiative in avodas Hashem?
While on the sugya, I want to note a different point highlighted by R’ Tzadok. Kabbalas haTorah, Shiras haYam – these are distant events down the road of Moshe’s life. How can the Angels mentioned in the above sugya plead on behalf of baby Moshe based on the merit of deeds which he has not yet accomplished? The answer is that although events in our bechira-determined lives must unfold through the passage of time, k’lapei shemaya, from the perspective of Hashem’s yediya and our destiny, the future already exists. Future events exist and exert their influence in history even before they unfold before our eyes. (Compare with the Rogachover's idea that time exists as a single point k'lapei shemaya). R’ Tzadok brings other examples to illustrate this point. When Rashi tells us of Avraham or Lot celebrating Pesach, it is more than a celebrating in anticipation of a future event – it is celebrating because the event of Pesach has occurred already kelapei shemaya even if it had not yet unfolded before them.