What was Moshe worried about now? Of what importance was it to know the Name of Hashem that was currently relevant?
Ramban #1 (citing the Ibn Ezra): Should Yisrael ask, he wanted to know which Name of Hashem to cite, because Hashem does not perform miracles with the Name Shakay, 1 only with Havayah (the Great Name of Hashem). 2
Ramban #2: Since Hashem had not indicated with which Midah He would appear in Egypt, Moshe wanted to know whether it would be with Midas ha'Din (symbolized by the Name Shakai), with which He wrought hidden miracles; or with Midas Rachamim (symbolized by the Name Havayah), with which He wrought open, supernatural miracles. 3
Ramban #3 (citing Chazal): With referring to Matan Torah, when Yisrael would ask for a more intimate relationship with Hashem, 4 he was now asking Hashem to reveal to him His great Name, in order to answer them when the time came.
Seforno: A person's name reflects his intended 'format'. Consequently, if Yisrael would know what to call Hashem, they would know His plan of action. 5
Rashbam: He simply wanted to know Hashem's Great Name 6 in order to answer Yisrael should they ask.
Rosh: Moshe wanted to know if he should tell Yisrael the Perush of His great name.
The Name by which He had operated with the Avos (See Rashi at the beginning of Va'eira [6:3]).
See Ramban's objection to the Ibn Ezra's explanation. Rashi in Va'eira (6:9) explains that Moshe was actually taken to task for questioning Hashem at all.
Ramban: What prompted him to ask whether Hashem would change His tactics was the fact that Hashem had mentioned Matan Torah - which he knew would not be performed with the Name Shakai that had prevailed in the era of the Avos, but with the Name Havayah, with which He had created the world. See also Ba'al ha'Turim.
See Rav Chavel's notes.
See Ramban, Pasuk 12, DH 've'Hinei'.
Presumably this refers to its deeper meaning, as the Ramban explains according to some of the explanations that he cites.
וכי ישראל לא ידעו את שם ה' שהיה מורגל בפי האבות?
גור אריה (לקמן 3:14): שאלת ישראל הייתה באיזה ענין [-מידה] באה להם התשועה (שהרי ה' נקרא לפי פעולותיו), כי אם זה יהיה בשם המיוחד הם ידעו שזו תהיה ישועה שלימה- בלי צער. 1
מהר"ל, גבורות ה' (פכ"ה עמ' ק"ו ד"ה וכאשר תעמיק): הטענה הייתה שכדי להיות קרוב לה' וראוי לגאולה, עליו לדעת לא רק את השם, אלא גם את סוד שמו, ועל זה ישאלו אותו.
מהר"ל, דרוש לשבת הגדול (סוף הגדה של פסח, עמ' רי"א): משה חשש שלא יאמינו לו כי ה' נעלם מעיני הבריות. 2