וַיִּקְרָ֨א אֵלָ֜יו מַלְאַ֤ךְ יְהוָה֙ מִן־הַשָּׁמַ֔יִם וַיֹּ֖אמֶר אַבְרָהָ֣ם ׀ אַבְרָהָ֑ם וַיֹּ֖אמֶר הִנֵּֽנִי׃
Ale zawołał nań anioł Wiekuistego z nieba, i rzekł: "Abrahamie! Abrahamie!" a rzekł: "Oto jestem!"
Rashi on Genesis
אברהם אברהם ABRAHAM, ABRAHAM — The repetition of his name is an expression of affection (Genesis Rabbah 56:7).
Kli Yakar on Genesis
Avraham, Avraham: An expression of love. And that which He did not call him twice the first time, [as] an expression of love, is because his love was still not known to all those that come to the world - perhaps he would not pass the test. But after he passed the test, [the love that was] beyond [that of] others was then apparent with tremendous clarity and power in the eyes of everyone. Hence, he [then] called him "Avraham, Avraham," [as] an expression of love - since this test was for the benefit of the one tested, to make known his love.
Radak on Genesis
ויקרא...מן השמים, he heard a voice without seeing a visual image.