Then you might want to look at Simula as well. As much as the term "object oriented" was invented in conjunction with Smalltalk, a lot of the basic concepts (classes, objects...) came from Simula (but not closures).

Blocks are one of the most important concepts of Smallalk. Every control structure is done via blocks in Smalltalk, even if/else is a method (message) on a boolean object, that takes two blocks as arguments: one for the 'true' case and one for the 'false' case.