The Vilna Gaon writes that Mordechai did not get up as if Haman were not even there.
The Ohel Moshe reminds us that Nefesh HaChaim (3:12) writes that a powerful spiritual power we have is to internalize the idea that no influence can affect us besides H-Shem. Mordechai’s believing this is one reason he refuses to even rise for Haman.
The Maharal writes the two actions of standing and stirring refer to Mordechai giving no sign of respect to either Haman, nor the idol he had constantly about him. He quotes the Midrash (Esther Rabbah 7:8) that Mordechai felt Haman made himself into an idolatry. In other words, borrowing a phrase from Yeshaya (2:24) such a person has “his soul in his nose,” or considers his own self-aggrandizement before anything else. For this self-worship is what Mordechai could not stir.
Rebbetzin Heller writes that when the Alter Rebbe of Lubavitch was is Russia, he quoted a Talmud (Sanhedrin 74a-b) that there are three things for which Jews should give up their lives to avoid transgressing. Put simply, these three “cardinal sins” are idolatry, adultery, and murder. However, that is only true under regular circumstances. However, if a nation attempts to destroy Judaism altogether, even the “smallest” of sins cannot be committed under threat of death. Therefore, in communist Russia too, where their laws added up to a struggle against Judaism, all of their laws could be ignored.
In an interesting gematria, the phrase v’lo kam v’lo za (“he did not rise and he did not stir”) (6+30+1+100+40+6+30+1+7+70=291) less the two mentions of v’lo (“and he did not”) (6+30+1=37×2=74) is equivalent to 217, the numerical value of eretz (“land”) (1+200+90=291). Perhaps this indicates that Mordechai’s refusal to do these actions helped the Jews merit re-entry into the Land of Israel in the following Persian reigns.