The suit is the modern gentleman's armour.

Harry Hart: [Quoting 威廉 Horman] "Manners maketh man." Do you know what that means? Then let me teach you a lesson.

Harry Hart: Now, my point is that the lack of a silver spoon has set you on a certain path that you needn't stay on. If you're prepared to adapt and learn, you can transform.
Gary 'Eggsy' Unwin: Yeah, like in 'My Fair Lady'.

Harry Hart: The suit is the modern gentleman's armour. The Kingsmen are the new knights.

Harry Hart: Nonsense. Being a gentleman has nothing to do with the circumstances of one's birth. Being a gentleman is something one learns.
Gary 'Eggsy' Unwin: Yeah, but how?
Harry Hart: Alright, first lesson. You should have asked me before you took your seat. Second lesson: How to make a proper 馬丁i.