God of the Living

Mark 12:26-27

The argument is better understood as a reflection on the character of the covenant God whom Moses encountered, a God who through his new name 'I AM' is revealed as the living God, the ever present helper and deliverer of his people. If such a God chooses to be identified by the names of his long dead servants, Abraham, Isaac and Jacob with whom his covenant was made, and whom he committed himself to protect, they cannot be simply dead and forgotten.  

... it's basis, far from being merely the tense of a verb, is in the fundamental theological understanding of Yahweh, the living God, and of the implications of his establishing an 'everlasting covenant' with his mortal worshippers.  

'God of the dead' is not a term which is appropriate to Yahweh as he is revealed in the book of Moses. 

The Gospel of Mark (The new international Greek testament commentary) p471-2