^^^^^^^ CB: It is difficult to imagine the working class struggling through to socialism if it is depressed and despirited. Good espirit de corps or morale are necessary conditions for the victory of the proletariat over the bourgeoisie. So, Marx and Engels' peptalk to the proletariat is applying a principle of materialist psychology.
One task of working class partisan rhetoricians is to find a new narrative inspiring enthusiasm.
So, comrades come rally !
Espirit de corps refers to the morale of a group.
http://en.wikipedia.org/wiki/Morale
Morale
Morale, also known as esprit de corps when discussing the morale of a group, is an intangible term used for the capacity of people to maintain belief in an institution or a goal, or even in oneself and others. The second term applies particularly to military personnel and to members of sports teams, but is also applicable in business and in any other organizational context, particularly in times of stress or controversy.