Why is it written? It is deliberately superfluous to signal a gezeirah shavah (i.e., "identity"), viz.: It is written here (in Exodus) "Hebrew," and there (in Devarim) "Hebrew." Just as there, "Hebrew" refers to the servant (and not to the master); here, too, "Hebrew" refers to the servant (and not to the master). And though there is no proof for this (i.e., that "servant Hebrew" is to be understood as "a servant who is a Hebrew" (and not as "the servant of a Hebrew"), there is support for it, viz. (Exodus 5:3) "The G–d of the Hebrews revealed Himself to us"—(the G–d) of "Avram the Hebrew" (Genesis 14:13).