...is the difference between a sigil and a manifesto. In other words: the artwork has had just enough of its own construction obscured to become (as TS Eliot put it) universal, an aesthetic object; but still embodies the original intent.
Propaganda and agitation are transitory, art is eternal - its effect is therefore more diffuse but potentially far deepr. Andrew Eldritch's "Vision Thing" was about Bush41, but it works equally well as an indictment of Bush43 - if you know how to look at it. Both are necessary in our struggle for change.
I think I'm reproducing insights from Trotsky's Literature and Revolution in a new form. Whatever, the question is to what use this insight can be put.