שמות פרק טו, א אָז יָש יר-משֶה וּבְנֵי י שְרָאֵל אֶת-הַש ירָה הַזֹאת
It is a well known question that this verse uses the future tense for the action of singing the song, and not the past tense that “they sang”. Rabbi Epstein explains that the Torah was hinting to the future generations that would live in Galus, that even in their times miracles would continue to occur that would warrant special songs of praise. At those times, the Jews should not ascribe these miracles to the natural processes, but that these miracles are directed by HaShem, just enclothed in the natural processes. This concept is especially connected to Purim. Thus, the Medrash says that when all the holidays would be nullified, the days of Purim would not be nullified. This is not referring to the nullification of the holiday itself, but that the miracles associated with each holiday would be overlooked in the times of Galus, yet the miracle of Purim that occurred in apparent natural circumstances would continue to be recognized as a miracle.
