The im-possible call to justice is undeconstructible because it exceeds, or is the basis of, any deconstruction of actual, achievable futures and positive laws. But it is precisely this im-possibility that gives deconstruction its passion. Derrida does not disappoint. You cannot address the other, speak to the other, without an act of faith, without testimony. And this universal structure of faith is an undeconstructible that Derrida calls the messianic structure or messianicity.
Someone is to come, is now to come.
Justice and peace will have to do with this coming of the other, with the promise. Each time I open my mouth, I am promising something. When I speak to you, I am telling you that I promise to tell you something, to tell you the truth. Even if I lie, the condition of my lie is that I promise to tell you the truth. This messianic structure, or messianicity, has everything to do with faith.