Why does Marjane want to be "the last prophet?" What would be the purpose of being "justice, love, and the wrath of God all in one?

There are drawings of some of the earlier prophets and in Marjane’s vision, these prophets question whether a woman can also be a prophet. She says that she had wanted to be a prophet “because our maid did not eat with us. Because my father had a Cadillac. And, above all, because my grandmother’s knees always ached.” Her grandmother is the only person that knows of her holy book and her rules that all should have cars, that maids should eat with others, and that “no old person should have to suffer.” When her grandmother questions her on how she will make it so that no old person will suffer, she says, “It will simply be forbidden.”