Irony in Doctor Faustus

Faustus's grand ideas of enacting whatever magic he wishes and commanding ultimate power in the world here devolves into dedicating himself to a higher power. Ironically, thought Faustus initially turns to black magic because he believes it will give him the most power, it takes away all of his power and makes him a servant to the devil.

"Chary" means dearly or carefully. This statement is ironic because Faustus did not keep his life or his soul carefully.

This is another instance in which we see Faustus unable to execute his own magic. He controls Mephistophilis, but wields no power of his own. Ironically, Faustus sells his soul for power and gains none.