In regard to the Song at the Sea, Rashi on Shemos (15:1) teaches that a letter “yud” in front of a verb indicates the intent of the subject. In the Sfas Emes’s understanding of this verse, Mordechai’s actions indicate that he would not bow. It was an impossibility for him, so remotely distant from his normative code and conduct. The Chofetz Chaim teaches that this, too, teaches the important of avoiding compromising morals.
The Sfas Emes also teaches that this verse is prophetically promising that, in every generation, there will be someone who will not bow. Jews have and always will have at least one person who keeps to what is true. Ultimately, this is going to be Moshiach, may he come soon.