Here's spring come, and the nights one makes up bands To roam the town and sing out carnival, And I've been three weeks shut within my mew, A-painting for the great man, saints and saints And saints again. I could not paint all night— Ouf! I leaned out of window for fresh air. (45-50)
It must really be a bummer to be Lippo, cooped up in his "mew" (a confined area, or a cage that a bird is trapped in) during the carnival season, when non-Church types are out partying it up. There's a double sense of confinement here: he's confined by the walls, but also by having to paint the saints—the subjects that the Prior and others want him to focus on.
On Jerome knocking at his poor old breast With his great round stone to subdue the flesh (73-74)
St. Jerome is also stripped of his freedom, at least as it relates to fleshly desires. Here, he confines those desires by harming himself with a "great round stone." Those saints were super-serious about getting right with God.
I did renounce the world, its pride and greed, Palace, farm, villa, shop, and banking-house, Trash, such as these poor devils of Medici Have given their hearts to—all at eight years old. (98-101)
At the tender age of eight years old, Lippo's freedom is basically stripped away from him when he's forced to take vows to avoid starving to death. Because of this, he gives up the "Palace, farm, villa, shop, and banking-house," all of which symbolize the worldly activities he's vowing to avoid for a life of contemplation.
Do you feel thankful, ay or no, For this fair town's face, yonder river's line, The mountain round it and the sky above, Much more the figures of man, woman, child, These are the frame to? (286-290)
Lippo's artistic imagination allows him some level of freedom from his monastery and his vows. He can imaginatively explore worldly places and subjects in his art, which gives him at least the fantasy of escape. Check out how he describes these scenes as if they are already works of art: "figures" and "frame."
Well, all these Secured at their devotion, up shall come Out of a corner when you least expect, As one by a dark stair into a great light, Music and talking, who but Lippo! (359-363)
Lippo literally paints himself into a corner of his masterpiece, "The Coronation of the Virgin," which he is planning out right now. While this seems like a moment of confinement, it's actually symbolizes freedom, since he's subversively adding in some realism (secretly inserting himself) into what appears to be an otherwise highly conventional painting that would make the Prior proud. Go, Lippo!