Do you mean to ask how the first possibility differs from the other two in the article's last section? The infinite series is unlimited, but the second possibility is that the universe is limited but incomplete, irrational, or absurd. (This is tricky, since finitude might imply a rational order.) The third is that the universe is ordered and rational but beyond anyone's comprehension.

But as to your question, an infinite series would be incomprehensible as a whole, even though each of its parts might be explainable as arising from a former one. But infinite series aren't entirely inexplicable, since we have the mathematical concept of infinity from Cantor. But a real (as opposed to potential) infinite series would indeed be wild and vast. Our ground-based intuition is that everything has a beginning, a middle, and an end.