"I will live in the whole of Beauty, and here it shall be mine." It is the aspiration of Aprile.
"Then, having this perfect human soul, master of all powers, I shall break forth, at some great crisis in history, and lead the world." It is the very aspiration of Sordello.
But when he tries for this, he finds failure at every point.

Everywhere he is limited; his soul demands what his body refuses to fulfil; he is always baffled, falling short, chained down and maddened by restrictions; unable to use what he conceives, to grasp as a tool what he can reach in Thought; hating himself; imagining what might be, and driven back from it in despair.
Even in his love for Pauline, in which he has skirted the infinite and known that his soul cannot accept finality--he finds that in him which is still unsatisfied.
What does this puzzle mean?
"It means," he answers, "that this earth's life is not my only sphere, Can I so narrow sense but that in life Soul still exceeds it ?" Yet, he will try again.

He has lived in all human life, and his craving is still athirst.

He has not yet tried Nature herself.

She seems to have undying beauty, and his feeling for her is now, of course, doubled by his love for Pauline.