Unlike another question that asks about the vague prophecy Rivkah was given about her twins, I ask specifically about Itzhak's statement to Esav:
... וְאֶת־אָחִיךָ תַּעֲבֹד ...׃ - And you shall serve your brother; Genesis.27.40
As I can see, most commentators skip this part of Isaac's prophecy. Unlike the former, this has a proper grammatical form "את אחיך" similar to "אֶת ה' אֱלֹהֶיךָ תִּירָא אֹתוֹ תַעֲבֹד", meaning serving and worshipping. And unlike the former, that spoke of either of them, this was addressed to Esav subserving him to Yaakov.
Was it really a blessing or a prophecy? If a blessing, what kind of blessing is that? If a prophecy, what does this mean for Esav and when was it fulfilled?