הן בני ישראל. לפי הפשט לא שמעו אלי. וא"ת כי הניחו מלשמוע מקוצר רוח וגו' לכך הוצרך לומר ואני ערל שפתים. אי נמי שמא משה לא היה יודע מה שאמר הכתוב מקוצר רוח וגו' ושמעתי מהר"י מלישבונ"ה שהיה מפרש הק"ו שפירש"י כלומר הן בני ישראל וגו' אף מקוצר רוח שעליהם ואני אומר להם שאני בא מאת הקב"ה לפדותכם מן השעבוד ואדם שהוא בבית הסוהר ושומע שבא אדם לפדותו הוא יוצא ושמח לקראתו ושומע לקולו והם לא הטו אזנם לשמוע אלי כל שכן שפרעה שאני בא להפקיע שיעבודו שלא ישמע אלי: הן בני ישראל לא שמעו אלי, “seeing that(even) the Children of Israel do not listen to me, etc.” According to the plain meaning of the text what Moses is saying is that the people do not listen to him, so what chance is there that Pharaoh would listen to him. In the event that one would excuse their failure to listen to him to their state of mind, i.e. they did not have a chance to indulge in day dreams, he adds that he attributes their failure to listen to him to his speech impediment, and therefore does not blame them. Alternately, perhaps Moses was not aware of the Torah having told us, the reader, that the reason why the people did not listen to him was their state of mind, i.e. impatience. I have heard from my teacher a Rabbi from Lisbon, that what Rashi meant when describing Moses’ logic here as unassailable, that the reason given as their state of mind, was an additional reason. His logic went as follows. Normally, when a potential redeemer promises his people that he has come to redeem them from slavery, they will be overjoyed. Seeing that the Israelites’ reaction to his message had been so negative, how much more negative would Pharaoh’s response be to their demanding a holiday!