the mental part of me had been nourished in florence by excellent teachers of latin , greek , philosophy and theology , and i had been deep into the boys ' pageants and plays of the city , often taking the leading parts in the dramas presented by my own confraternity in my uncle 's house , and i knew how to solemnly portray the biblical isaac about to be sacrificed by the obedient abraham , as well as the charming angel gabriel discovered by a suspicious st. joseph with his virgin mary .