I. This world is not conclusion

THIS world is not conclusion;
        A sequel stands beyond,
Invisible, as music,
        But positive, as sound.
It beckons and it baffles;
        Philosophies don't know,
And through a riddle, at the last,
        Sagacity must go.
To guess it puzzles scholars;
        To gain it, men have shown
Contempt of generations,
        And crucifixion known.