What is the difference betwen a "messenger" and a "courier"

I was making a point of the irony, not seeking to insult our package carrying bretheren.

Another irony often commented upon is that couriers, who are a manifestation of counter culture, make their living carrying the deeds and documents of the archdeacons of capitalist culture; bankers and lawyers.

Then irony of ironies,said bankers and lawyers start to emulate cycle-couriers!