"And He called to Moses" (Leviticus 1:1). But to Adam He did not call, for it is written, "And the LORD God called to the man" (Genesis 3:9); yet there is no disgrace for a king to speak with his tenant farmer. "And the LORD spoke to him"; and with Noah He did not first call, for it is written, "And God spoke to Noah" (Genesis 8:15); yet there is no disgrace for a king to speak with his herdsman. "And He called to Moses" - but to Abraham He did not call, for it is written, "And the angel of the LORD called to Abraham" (Genesis 22:15); yet there is no disgrace for a king to speak with his innkeeper. "And He called to Moses" - and not as with Abraham. Concerning Abraham it is written, "And the angel of the LORD called to Abraham," the angel calls and the Speech speaks; but here the Holy One, blessed be He, said: I am the One who calls and I am the One who speaks, as it is said, "I, even I, have spoken; indeed I have called him; I have brought him, and he shall make his way prosper" (Isaiah 48:15).
Why the Holy One Both Called and Spoke to Moses
Yalkut Shimoni on Torah 428:2
וַיִּקְרָא אֶל מֹשֶׁה, וּלְאָדָם לֹא קָרָא "וַיִּקְרָא ה' אֱלֹהִים אֶל הָאָדָם" אֶלָּא אֵין גְּנַאי לַמֶּלֶךְ לְדַבֵּר עִם אֲרִיסוֹ, "וַיְדַבֵּר ה' אֵלָיו", וְעִם נֹחַ לֹא דִּבֵּר, "וַיְדַבֵּר אֱלֹהִים אֶל נֹחַ", אֶלָּא אֵין גְּנַאי לַמֶּלֶךְ לְדַבֵּר עִם נַקְדּוּדוֹ וַיִּקְרָא אֶל מֹשֶׁה וּלְאַבְרָהָם לֹא קָרָא (שם כב, טו) "וַיִּקְרָא מַלְאַךְ ה' אֶל אַבְרָהָם" אֶלָּא אֵין גְּנַאי לַמֶּלֶךְ לְדַבֵּר עִם פֻּנְדָּקִי שֶׁלּוֹ, וַיִּקְרָא אֶל מֹשֶׁה, וְלֹא כְאַבְרָהָם, בְּאַבְרָהָם כְּתִיב "וַיִּקְרָא מַלְאַךְ ה' אֶל אַבְרָהָם" הַמַּלְאָךְ קוֹרֵא וְהַדִּבּוּר מְדַבֵּר, בְּרָם הָכָא אָמַר הַקָּדוֹשׁ בָּרוּךְ הוּא אֲנִי הַקּוֹרֵא וַאֲנִי הַמְדַבֵּר שֶׁנֶּאֱמַר (ישעיה מח, טו) "אֲנִי דִּבַּרְתִּי אַף קְרָאתִיו הֲבִאֹתִיו וְהִצְלִיחַ דַּרְכּוֹ".