What is advent? Advent is a dimension of the future that is ordinarily foreclosed to both wider culture and to thought. It can be argued that the possibility of advent is rational - that it is indeed the peak of rationality. Given what we know about the real and the nature of desire, we can say that the most rational desire is a desire for advent. But human beings have a tendency to swim in a murky para-reason, using reason to get to a certain point, but then at that point abandoning it (traditionally the sages and philosophers identify this point with honor, wealth, power). I'm just briefly and casually glossing this topic right now, but I will return to it. The main resources for constructing an idea of rational advent are Meillassioux, Moltmann and Rosenzweig.
What to say about the shame associated with messianism? Painting with the broadest of brush strokes, we can say that it is an effect of the same suture, the same ARMISTICE that forecloses speculation about cosmogony - which is to say that it amounts to ideology. The ideology of the VORIZENIC ARMISTICE is an inhibition of the imagination via a subtle shaming of the effort to join reason and the divine that thwarts freedom, wisdom and power: no cosmogony, no eschatology