But Isaac who was indicative of contraction, his name was not changed from world to world and therefore his name didn't change. And therefore Avram couldn't have children until it spread in this world. But Jacob who is the middle of the attributes between kindness and greatness which indicate spreading and contraction, from the side of kindness he should have changed his name but from the side of contraction he need not change it, therefore the name of Jacob was not uprooted , and he could have children before he was Israel. And when we are called Israel we are at the highest level for it indicative of the kindness when it is spread and came to this world through contraction. They represent love.
Love requires contraction.
The change of name indicates contraction. Isaac is greatness. Greatness is contraction. Contraction needs no contraction into a new name. Jacob was a mixture of love and greatness.