Even if there aren't any demons around to offer us the special powers and abilities for the price of our souls, still, the above statement works today and has probably carried a lot of meaning throughout different times. In order to see how, we need to look at the process from the opposite angle.
A person with a special talent or ability. Such a person has gained this talent, say a great musician or an exceptional sword fighter, through extensive practice and focus. Innate skills help but are usually not enough and some proper amount of time needs to be spent on mastering the ability (10,000 hours according to many people including the outliers book by Malcolm Gladwell). The only way for someone to find the discipline to follow such focused practice and hard work is only through love. Love for the specific craft or skill. A love which will lead the person into the psychological state of "flow" that will make him forget about the passing of time, his needs, social or physiological.
Events related to this person's goal, which is to return to the state of flow, by practicing the craft or art (music or swordsmanship) will matter and will pull the attention of this person, all else can be ignored and seem redundant.
Great feeling for this person, but how does the society view such a specialist? "Anti-social" is a polite word for describing this person, weird or selfish are what follows and it can go on until this person can be regarded as "Not a Person" or also known as a person with out a soul. How best to describe a person with no soul but to say that he has sold his soul to the devil. This way the society can feel relieved about the reasons for the exceptional talent too. In return of his soul, the devil has offered him such skills. Oh ... how dangerous this soul less creature should be! Lets define a mighty devil and be afraid of it in order to justify our own laziness. We were not able to achieve anything in this world but we should not worry since we have a soul that will live like a king in another world just because we deserve so but this man is really happy and able and different from us so he must have sold his soul and there is no eternal happiness for him. We are fine, we can sleep well, it is ok to be lazy and afraid.
Nietzsche's Uberman has been described as a free and powerful man which is frightened by normal people. Frightened? Sure, why not, this is a person following his own will, a will to follow the inner love, to focus on the inner desire and achieve special abilities that can be only achieved by listening to your heart only. Listening to your heart is usually in contrast with the structures and rules imposed by the society so you will resemble an outlaw, you will not follow the pre-specified routes designed for you in order to achieve what you feel needs to be achieved. To them, you seem different, anyone different from them should not be a human, or at best a human with no soul, someone to be afraid of, someone who has dealt with the devil. Keep away, keep away.
If you're serious about doing something and do not want to be regarded as the guy who has a diabolic contract hidden in a chest somewhere, you better learn how to be a good actor!