In the parasha of Vayishlach Yaakov’s name is changed twice. Both times his new name is Yisrael. He is morphed twice from the ‘One Who Grasps Ankles’ to ‘the One Who Wrestles with G-d.’ The first time he is renamed by the adversary he wrestles with throughout the night (Gen. 32:29). On the second occasion he is renamed by G-d Himself (35:10). So why is his name change presented to us twice and why on these two occassions?
Ramban on 35:10 notes that before assigning Yaakov his new name, God states plainly "your name is Yaakov," since it wasn't the angel's mission to change Yaakov's name.
R' Samson Raphael Hirsch on 32:29 takes this discrepancy a step further by noting a difference between the verbs in the two verses. The angel says "לא יעקב יאמר עוד שמך", which R' Hirsch interprets as "not Jacob shall they name be expressed any more,"1 while God says "לא יקרא שמך עוד יעקב", which R' Hirsch interprets as "thy name shall no longer be called Jacob."
According to R' Hirsch, the angel's message is not that Yaakov's name is changing, but that the same name Yaakov would now be understood as Yisrael, meaning "God is the All-conquering one." When people see a "Yaakov," apparently a weak member of the "heel" of society, miraculously overpowering stronger-looking foes, it demonstrates that God is all-powerful, and that He can and does intervene to help those who are close to him vanquish any power. When this happens, "Yaakov" teaches the world that "Yisrael."
R' Hirsch doesn't return to the topic on 35:10 to explain why God formalizes the name change at this point. I would suggest that now that Yaakov's family has attained it's full strength at 12 sons, it's hard to see Yaakov personally as a mere heel-grabber anymore. He is clearly the head of a mighty clan. Now, God says, the "Yisrael" message is apparent not in individual surprising victories by a weak-looking Yaakov, but by the evolution of previously-weak Yaakov into the mighty proto-nation of Yisrael.
1. As translated into English by Isaac Levy