Answer:
It is important to know that Robin and Ralph are innkeepers:
* to show contrast with Faustus, who is a doctor
* to indicate that the two men are members of the lower class
Step-by-step explanation:
That they are innkeepers from a lower class help to demonstrate that even when Faustus is an academic and well-prepared person, falls for simple tricks like the ones Robin al Ralph perform and that is not something that Faustus is happy about since he considers them inferior due to the abilities he has acquired after selling his soul.