The explanation given by Alt in "Der Gott der Vaeter, that the ancestors
of the Israelites worshipped tribal gods, still holds. Ex. 6:3
illustrates the change in deity, from a tribal to a national one; Ex. 3
gives the Elohistic version of the same change.

In the latter case, the previous deity is simply called the god of the
fathers Abraham, Isaac and Jacob", whereas in Ex. 6 he is called El
Shaddai.
Whereas Alt considered El Shaddai of the Priestly Code as late, today
there is ample evidence, from Deir Alla and even Mari, that Shaddai is
an early deitry.
--
Jonathan D. Safren
Dept. of Biblical Studies
Beit Berl College
Beit Berl Post Office 44905
Israel