I can't see what you are saying

Hashem appeared to Miriam and Aharon to respond to their criticism of Moshe. Hashem addressed them:

וַיֹּ֖אמֶר שִׁמְעוּ־נָ֣א דְבָרָ֑י

Rashi comments:

אֵין נָא אֶלָּא לְשׁוֹן בַּקָּשָׁה

Why should Hashem have to make a special appeal to them to listen? Isn't it the aspiration of every navi to receive the dvar Hashem?

Ohr haChaim: צריך לדעת למה הוצרך לומר כן ודאי כי ישמעו את אשר ידבר, עוד צריך לדעת אומרו תיבת נא כי לא יוצדק לומר האדון לעבדו לשון בקשה.

He gives multiple answers, among them that by saying "Listen to what I am saying" the implication hinted at is that they had not previously been listening, or had not listened and correctly interpreted the dvar Hashem.

A couple of years ago I quoted a piece from the Tiferes Shlomo (I know it's wrong to play favorites, but this is one of my favorite pieces) that he repeats a few places in chumash. When Hashem asked Adam haRishon אַיֶּֽכָּה, Adam responded אֶת־קֹֽלְךָ֥ שָׁמַ֖עְתִּי בַּגָּ֑ן וָֽאִירָ֛א כִּֽי־עֵירֹ֥ם אָנֹ֖כִי. The Tif Shlomo explains that when Klal Yisrael accepted the Torah, Chazal tell us that we had the ability to be רואים את הקולות. It was a visual as well as an auditory experience. This was the level that Adam was on before the cheit. After the cheit, when Adam experienced אֶת־קֹֽלְךָ֥ שָׁמַ֖עְתִּי בַּגָּ֑ן -- he heard but did not see the kol Hashem -- he realized that he had fallen from the level he had been on beforehand.

Later in Braishis, how did the brothers know that the person speaking to them was indeed their long lost brother Yosef? Yosef told them (45:12) וְהִנֵּ֤ה עֵֽינֵיכֶם֙ רֹא֔וֹת וְעֵינֵ֖י אָחִ֣י בִנְיָמִ֑ין כִּי־פִ֖י הַֽמְדַבֵּ֥ר אֲלֵיכֶֽם: When he speaks, they don't just hear his voice, but וְהִנֵּ֤ה עֵֽינֵיכֶם֙ רֹא֔וֹת, they see it as well. His words are dvar Hashem, not milei d'alma, as their own experience proves.

Here too in our parsha, Hashem was indicating to Miriam and Aharon just how far they had fallen. שִׁמְעוּ־נָ֣א דְבָרָ֑י -- you can hear the words, but you won't experience seeing them the way you should have, the way Moshe does.

I did not see it in the Tiferes Shlomo, but maybe one can suggest that later in parshas Chukas, when Moshe addressed Bn"Y with the words שִׁמְעוּ־נָא֙ הַמֹּרִ֔ים when they were clamoring for water, this was the knock on them.  Since שׁכינה מדבּרת מתוך גורנו, when Moshe spoke they should have not just heard, but they should have seen the dvar Hashem. Because of their rebelliousness, the people were denied this experience.