When Hashem appeared to Moshe at the burning bush in parshot shamot perek gimil why did he call Moshe's name twice? He could have just said "moshe" ONCE!
The Zohar (Bamidbar 138a and 187b) points out that this repetition is further unique in that the two "Moshe"s are not separated by a pesik (vertical line), unlike other repeated names in Tanach ["Avraham | Avraham" (Gen. 22:11), "Yaakov | Yaakov" (ibid. 46:2), "Shmuel | Shmuel" (I Sam. 3:10)].
This, says the Zohar, was because Moshe was perfect from birth (i.e., he was the same "Moshe" throughout his life), unlike the others who, at the time when Hashem called them, achieved something that they hadn't previously had.
We often see throughout the Tanach that Hashem calls someones name twice. We learn from the Mafarshim that this means Hashem is saying, 'I love you-do not worry my next request is not a hard one.' Often the double name is followed by 'Hinneni", here I am, meaning that I will do your next request without even knowing what it is. This is what we see with Moshe at the burning bush. Hashem calls his name twice meaning I love you and Moshe responds Hinneni without knowing the request. As we continue the story Hashem's request is not an easy one and does not seem to follow the principles set out above. However, a careful reading of the text shows that Hashem's first request and the request to which the double name and the Hinneni refer to is in fact the removal of Moshe's shoes. Hashem continues, using Moshe's name only once when he requests that Moshe go down to Egypt to speak with Pharoh.