After Cantor, mathematicians realised that infinities can be graded by size (cardinalities). But just as we view the naive infinite as bigger than any finite number, is there an 'infinite' greater than any infinite?
But then the same pattern can carry on, in which case we are actually no nearer the absolute infinite than we were to begin with, that is Cantors mathematics of the infinite cannot do real justice to the idea of the Infinite.
To be more explicit, the Large Cardinal Axioms extend ZFC by postulating ever higher 'Cardinalities'. "However the observation that large cardinal axioms are linearly ordered by consistency strength is just that, an observation, not a theorem. (Without an accepted definition of large cardinal property, it is not subject to proof in the ordinary sense)...Saharon Shelah has asked, "[i]s there some theorem explaining this, or is our vision just more uniform than we realize?" Woodin, however, deduces this from the Ω-conjecture, the main unsolved problem of his Ω-logic."