From Artscroll on the Malbim 

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וַיְדַבֵּ֥ר אֱלֹהִ֖ים אֶל־מֹשֶׁ֑ה וַיֹּ֥אמֶר אֵלָ֖יו אֲנִ֥י יְהֹוָֽה׃

God spoke to Moses and said to him, “I am יהוה.

https://www.sefaria.org/Exodus.6.2

וָאֵרָ֗א אֶל־אַבְרָהָ֛ם אֶל־יִצְחָ֥ק וְאֶֽל־יַעֲקֹ֖ב בְּאֵ֣ל שַׁדָּ֑י וּשְׁמִ֣י יְהֹוָ֔ה לֹ֥א נוֹדַ֖עְתִּי לָהֶֽם׃

I appeared to Abraham, Isaac, and Jacob as El Shaddai, but I did not make Myself known to them by My name יהוה.

https://www.sefaria.org/Exodus.6.3

Until now every time that Hashem spoke to Moshe, the Torah had stated 'vayomer Elokim, 'and God said.'

Here, for the very first time, the Torah uses the phrase

'vayedabeir Elokim,' 'and God spoke.'

This shift in language, as will be explained, marks the elevation of Moshe's prophetic level from a level that until this point had been comparable to that of the other prophets. 

From now on, however, Moshe's prophetic experience would begin its ascent to the highest possible level, to that of the 'Prophet of Torah,' level forever distinguishing Moshe from all other prophets.

Among the differences between 'dibur' ('speaking') and

'amirah' ('saying') is that dibur refers to the act of speaking, especially to speaking at length,' while amirah refers to the mes-sage, oral or otherwise imparted.

When the Torah, therefore, states that 'Hashem spoke (va yedabeir) to Moshe saying (leimor)...,' the term 'va'yedabeir' implies that Hashem spoke to Moshe at length, revealing to him all the Torah's kabbalistic secrets and elaborating upon all the halachic particulars that were to comprise the unwritten, oral tradition.

See Menachot 29b, wherein Rabbi Akiva is recorded as having derived

'heaps upon heaps' of Torah laws from every jot and crownlike frill atop the letters in the Torah scroll.

'Leimor,' on the other hand, refers to the exact wording of the statements that Moshe would inscribe in the Torah scroll.

The verses of the Torah would serve as the amirah containing

— in 'shorthand' form — all the vast information conveyed to Moshe through 'dibur.'

Much as in English the phrase giving a 'speech' means to converse at length.

Understanding the above helps us understand why the phrase

'Hashem spoke to Moshe saying...' is used only in regard to Moshe, and not in regard to any other prophet. Only Moshe, as the Prophet of the Torah, heard 'dibur,' Hashem actually speaking, fully explaining the Torah's mystical, esoteric secrets as well as all of its complex halachic details. 

The sole exception, 'And Hashem spoke to Yehoshua saying...

(Yehoshua 20:1), does not disprove the rule, because the verses that follow are essentially a repetition of halachos which appear in the Five Books of Moses Communication

Amirah is sometimes used in Tanach allegorically, describing for example the nonverbal messages of inanimate objects (e.g., Iyou 38:35; Mishlei 30:16) whereas dibur always refers to actual vocalized speech (Malbim's commentary to Toras Kohanim, Siman 3).

Simply put, the phrase 'God spoke to Moshe and said,' is no redundancy. Rather, the verse is pointing out not only what Hashem said to Moshe, but that Hashem said it via 'dibur,' clear and instructive speech.

TWO LEVELS OF PROPHECY

As we explained in Parashas Vayeitzei, Moshe's elevated level of prophecy is indicated as well in a subtle shift in the verse's verb choice: 'I appeared to Auraham, Yitzchak, and to Yaakou...but My Name, Hashem, was not known to them.' The Zohars contrasts the two verbs used in this verse,

'appearing' as opposed to 'knowing': Hashem 'appeared to them,' a prophetic experience limited by visualization, but 'was not known to them.' Moshe's prophecy, via the 'aspeklaria me'ira,' the 'radiant prism,' brought him to the higher level of knowing, beyond that which any picture can describe.

TWO NAMES OF HASHEM

Our verse begins by referring to God as 'Elokim' and ends with 'I am Hashem,' which, as the Zohar explains, indicates the elevation of Moshe's prophecy to a new and higher level:

The name Elokim signifies God as working within nature through hidden miracles, which had been Hashem' s way

of relating to the Jewish People ever since the time of the

Patriarchs and until now, The Four-Letter Name of Hashem, the Tetragrammaton, 10 indicates Hashem's essence as totally above and beyond nature, pertorming miracles as novel as the creation of the world itself. This miraculous mode of running altairs was to be Hashem's way of relating to Moshe and to his generation,

starting now.

Informing Moshe of this new state of affairs served to answer Moshe's question 'why have you done evil to this nation?' (Shemos 5:23). Moshe thought that the redemption from Mitzrayim would come about through hidden miracles in a seemingly natural fashion like the dawning of a new day, and that as such it would arrive and grow gradually. Moshe therefore assumed that his mission to Pharaoh would result in at least some slight reduction in the Jewish suffering, and he questioned why the opposite had occurred.

Were the redemption to have occurred through God's

'Elokim' mode of working through nature, then Moshe would have been correct. By saying 'I am Hashem,' however, Hashem informed Moshe that the opposite was to occur, that the redemption would come about through the openly miraculous mode described by the Name 'Hashem'; and that, as such, it was fitting that the redemption come not gradually, but rather that it

burst forth from amid the height of

Jewish suffering, just as a newborn

emerges when the mother's travail

their lowest point, the reaches its.

Thus, in the previous verse Hashem told Moshe, 'now you shall see that which I will do to Pharaoh...' Specifically now that the Jewish People have reached

their lowest point would the redemption suddenly shine forth like a blinding light from out of the pitch darkness.

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