בראשית כב:יא פירוש: רש״י, כלי יקר, רד״ק והעמק דבר

אברהם אברהם ABRAHAM, ABRAHAM — The repetition of his name is an expression of affection (Genesis Rabbah 56:7).

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.

ויקרא...מן השמים, he heard a voice without seeing a visual image.