Why, throughout the Torah, does the Pasuk add the word "Leimor"?
Rashi: Refer to 6:12:1:1.
Ramban #1 (citing the R'dak): When it in connection with Yisrael, it means that Hashem spoke to Moshe to tell Yisrael; here it means to tell Par'oh. 1
Ramban #2: The Torah adds "Leimor" for clarity - particularly with regard to the prophesies of Moshe Rabeinu, 2 to whom Hashem spoke "mouth to mouth, and not in riddles" 3 (as opposed to all other prophets, whose prophesies were generally ambiguous and had to be deciphered).
See Ramban, who gives numerous examples where it is impossible to learn like that - one of them in Vayeitzei (31:29),where Lavan said to Ya'akov "v'Elokei Avichem Emesh Amar eilai Leimor"; another in Acharei-Mos (19:1 & 2) "Vayedaber Hashem El Moshe Leimor. Daber el B'nei Yisrael ... ".
Ramban: Though it pertains also to other people, who used the word 'Leimor' to make a clear statement (for example Lavan - Refer to 6:10:1:1* - who told Ya'akov that Hashem had spoken to him the previous night and had warned him in no uncertain terms, not to harm him (Ya'akov) and Yisrael - See Korach, Bamidbar 17:27, who vigorously complained to Moshe that all was lost.