The irony of Faustus' career lies in his tragic dilemma because while he signed away his life in blood for unlimited command of the cosmos, he was thereafter limited by Lucifer's constraints and, instead of gaining all command, Faustus was given magic tricks and left to dance with Seven Deadly Sins.
LUCIFER. sit down, and thou
shalt see all the Seven Deadly Sins appear in their proper shapes.
In meantime take this book; peruse it throughly,
And thou shalt turn thyself into what shape thou wilt.
This is the painful irony because he lost what he traded his soul to gain.
Faustus. All things that move between the quiet poles
Shall be at my command:
raise the wind, or rend the clouds;
Stretcheth as far as doth the mind of man;
A sound magician is a mighty god:
Faustus had mastered all knowledge available to him in economics, divinity, medicine and all other fields. Yet he found none that would occupy his attention for the rest of his life. He discarded them all. He chose the lines and circles and allure of magic aided by the demonic. He planned to have demons answer his beck and call and to fulfill all his wishes as though they were his servants: "my servile spirits."
Faustus did not reckon on the demonic reality requiring obedience to Lucifer. Yet, as the quotation in the Question Box shows, Mephistopheles himself was under command of Lucifer. To his surprise, Faustus found he was, too, under the command of Lucifer and, scared for the torments that might befall him in life, Faustus obediently gave up his ideas of grandeur and of knowledge of the cosmos and yielded to Lucifer and Mephistopheles's ideas of necromancy (magic).